From 9e2673ae2d90505ec8775b146773a8ccf1c7dbaf Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Fri, 12 Jun 2020 22:59:56 +0200
Subject: [PATCH 01/19] Fix identifier resolution

---
 boa/src/builtins/error/reference.rs        | 77 ++++++++++++++++++++++
 boa/src/environment/lexical_environment.rs |  1 +
 boa/src/exec/exception.rs                  | 13 ++++
 boa/src/exec/identifier/mod.rs             | 26 ++++++++
 boa/src/exec/mod.rs                        |  9 +--
 5 files changed, 119 insertions(+), 7 deletions(-)
 create mode 100644 boa/src/builtins/error/reference.rs
 create mode 100644 boa/src/exec/identifier/mod.rs

diff --git a/boa/src/builtins/error/reference.rs b/boa/src/builtins/error/reference.rs
new file mode 100644
index 00000000000..bed7c7a7b2e
--- /dev/null
+++ b/boa/src/builtins/error/reference.rs
@@ -0,0 +1,77 @@
+//! This module implements the global `ReferenceError` object.
+//!
+//! Indicates an error that occurs when de-referencing an invalid reference
+//!
+//! More information:
+//!  - [MDN documentation][mdn]
+//!  - [ECMAScript reference][spec]
+//!
+//! [spec]: https://tc39.es/ecma262/#sec-native-error-types-used-in-this-standard-rangeerror TODO
+//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError
+
+use crate::{
+  builtins::{
+      function::make_builtin_fn,
+      function::make_constructor_fn,
+      object::ObjectKind,
+      value::{ResultValue, Value},
+  },
+  exec::Interpreter,
+  profiler::BoaProfiler,
+};
+
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct ReferenceError;
+
+impl ReferenceError {
+  /// Create a new error object.
+  pub(crate) fn make_error(this: &mut Value, args: &[Value], _: &mut Interpreter) -> ResultValue {
+      if !args.is_empty() {
+          this.set_field(
+              "message",
+              Value::from(
+                  args.get(0)
+                      .expect("failed getting error message")
+                      .to_string(),
+              ),
+          );
+      }
+      // This value is used by console.log and other routines to match Object type
+      // to its Javascript Identifier (global constructor method name)
+      this.set_kind(ObjectKind::Error);
+      Err(this.clone())
+  }
+
+  /// `Error.prototype.toString()`
+  ///
+  /// The toString() method returns a string representing the specified Error object.
+  ///
+  /// More information:
+  ///  - [MDN documentation][mdn]
+  ///  - [ECMAScript reference][spec]
+  ///
+  /// [spec]: https://tc39.es/ecma262/#sec-error.prototype.tostring
+  /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/toString
+  #[allow(clippy::wrong_self_convention)]
+  pub(crate) fn to_string(this: &mut Value, _: &[Value], _: &mut Interpreter) -> ResultValue {
+      let name = this.get_field("name");
+      let message = this.get_field("message");
+      Ok(Value::from(format!("{}: {}", name, message)))
+  }
+
+  /// Create a new `ReferenceError` object.
+  pub(crate) fn create(global: &Value) -> Value {
+      let prototype = Value::new_object(Some(global));
+      prototype.set_field("message", Value::from(""));
+
+      make_builtin_fn(Self::to_string, "toString", &prototype, 0);
+
+      make_constructor_fn("ReferenceError", 1, Self::make_error, global, prototype, true)
+  }
+
+  /// Initialise the global object with the `ReferenceError` object.
+  pub(crate) fn init(global: &Value) {
+      let _timer = BoaProfiler::global().start_event("referenceerror", "init");
+      global.set_field("ReferenceError", Self::create(global));
+  }
+}
diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index 8e32c099457..829c168a186 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -213,6 +213,7 @@ impl LexicalEnvironment {
     }
 
     pub fn get_binding_value(&self, name: &str) -> Value {
+        dbg!(&self.environment_stack);
         self.environments()
             .find(|env| env.borrow().has_binding(name))
             .map(|env| env.borrow().get_binding_value(name, false))
diff --git a/boa/src/exec/exception.rs b/boa/src/exec/exception.rs
index ddef2e82ee1..b65ac99d62a 100644
--- a/boa/src/exec/exception.rs
+++ b/boa/src/exec/exception.rs
@@ -33,4 +33,17 @@ impl Interpreter {
         ))
         .run(self)
     }
+
+    /// Throws a `Reference` with the specified message.
+    pub fn throw_reference_error<M>(&mut self, message: M) -> ResultValue
+    where
+        M: Into<String>,
+    {
+        // Runs a `new ReferenceError(message)`.
+        New::from(Call::new(
+            Identifier::from("ReferenceError"),
+            vec![Const::from(message.into()).into()],
+        ))
+        .run(self)
+    }
 }
diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
new file mode 100644
index 00000000000..b81d2b37dca
--- /dev/null
+++ b/boa/src/exec/identifier/mod.rs
@@ -0,0 +1,26 @@
+use super::{Executable, Interpreter};
+use crate::{
+  builtins::value::{ResultValue, Value, ValueData},
+  syntax::ast::node::identifier::Identifier,
+};
+
+impl Executable for Identifier {
+  fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
+    let reference = resolve_binding(interpreter, self.as_ref());
+    match reference.data() {
+      ValueData::Undefined => Err(
+        interpreter
+          .throw_reference_error(self.as_ref())
+          .expect_err("throw_reference_error() must return an error"),
+      ),
+      _ => Ok(reference),
+    }
+  }
+}
+
+pub(crate) fn resolve_binding(interpreter: &mut Interpreter, name: &str) -> Value {
+  interpreter
+    .realm()
+    .environment
+    .get_binding_value(name)
+}
diff --git a/boa/src/exec/mod.rs b/boa/src/exec/mod.rs
index 4d8f25ed6c9..59052958516 100644
--- a/boa/src/exec/mod.rs
+++ b/boa/src/exec/mod.rs
@@ -7,6 +7,7 @@ mod declaration;
 mod exception;
 mod expression;
 mod field;
+mod identifier;
 mod iteration;
 mod object;
 mod operator;
@@ -502,13 +503,7 @@ impl Executable for Node {
             Node::Const(Const::String(ref value)) => Ok(Value::string(value.to_string())),
             Node::Const(Const::Bool(value)) => Ok(Value::boolean(value)),
             Node::Block(ref block) => block.run(interpreter),
-            Node::Identifier(ref name) => {
-                let val = interpreter
-                    .realm()
-                    .environment
-                    .get_binding_value(name.as_ref());
-                Ok(val)
-            }
+            Node::Identifier(ref identifier) => identifier.run(interpreter),
             Node::GetConstField(ref get_const_field_node) => get_const_field_node.run(interpreter),
             Node::GetField(ref get_field) => get_field.run(interpreter),
             Node::Call(ref expr) => expr.run(interpreter),

From f782a4dd0530148f034fe8045237c18c313d9f4a Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Fri, 12 Jun 2020 23:06:34 +0200
Subject: [PATCH 02/19] Debug

---
 boa/src/environment/lexical_environment.rs | 1 -
 boa/src/exec/identifier/mod.rs             | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index 829c168a186..8e32c099457 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -213,7 +213,6 @@ impl LexicalEnvironment {
     }
 
     pub fn get_binding_value(&self, name: &str) -> Value {
-        dbg!(&self.environment_stack);
         self.environments()
             .find(|env| env.borrow().has_binding(name))
             .map(|env| env.borrow().get_binding_value(name, false))
diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index b81d2b37dca..0df2c50cf0c 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -6,6 +6,7 @@ use crate::{
 
 impl Executable for Identifier {
   fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
+    dbg!(self.as_ref());
     let reference = resolve_binding(interpreter, self.as_ref());
     match reference.data() {
       ValueData::Undefined => Err(

From 7e152c65c6b146d10a99a2865eebdc42bc71fc9a Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Sat, 13 Jun 2020 14:54:37 +0200
Subject: [PATCH 03/19] Fix: define ReferenceError on global object

---
 boa/src/builtins/error/mod.rs  | 3 ++-
 boa/src/builtins/mod.rs        | 3 ++-
 boa/src/exec/identifier/mod.rs | 1 -
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/boa/src/builtins/error/mod.rs b/boa/src/builtins/error/mod.rs
index a6df97025be..d77030c4532 100644
--- a/boa/src/builtins/error/mod.rs
+++ b/boa/src/builtins/error/mod.rs
@@ -22,13 +22,14 @@ use crate::{
 
 // mod eval;
 pub(crate) mod range;
-// mod reference;
+pub(crate) mod reference;
 // mod syntax;
 pub(crate) mod r#type;
 // mod uri;
 
 pub(crate) use self::r#type::TypeError;
 pub(crate) use self::range::RangeError;
+pub(crate) use self::reference::ReferenceError;
 
 /// Built-in `Error` object.
 #[derive(Debug, Clone, Copy)]
diff --git a/boa/src/builtins/mod.rs b/boa/src/builtins/mod.rs
index 4e43b5268f7..8e8eb000a9b 100644
--- a/boa/src/builtins/mod.rs
+++ b/boa/src/builtins/mod.rs
@@ -21,7 +21,7 @@ pub(crate) use self::{
     array::Array,
     bigint::BigInt,
     boolean::Boolean,
-    error::{Error, RangeError, TypeError},
+    error::{Error, RangeError, ReferenceError, TypeError},
     function::Function,
     number::Number,
     regexp::RegExp,
@@ -47,5 +47,6 @@ pub fn init(global: &Value) {
     console::init(global);
     Error::init(global);
     RangeError::init(global);
+    ReferenceError::init(global);
     TypeError::init(global);
 }
diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index 0df2c50cf0c..b81d2b37dca 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -6,7 +6,6 @@ use crate::{
 
 impl Executable for Identifier {
   fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
-    dbg!(self.as_ref());
     let reference = resolve_binding(interpreter, self.as_ref());
     match reference.data() {
       ValueData::Undefined => Err(

From b50538bd2fafb1814146c4fdba7966a1cefe502b Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Sat, 13 Jun 2020 14:56:28 +0200
Subject: [PATCH 04/19] Format

---
 boa/src/builtins/error/reference.rs | 113 +++++++++++++++-------------
 boa/src/exec/identifier/mod.rs      |  27 +++----
 2 files changed, 71 insertions(+), 69 deletions(-)

diff --git a/boa/src/builtins/error/reference.rs b/boa/src/builtins/error/reference.rs
index bed7c7a7b2e..ff8c0aa26b5 100644
--- a/boa/src/builtins/error/reference.rs
+++ b/boa/src/builtins/error/reference.rs
@@ -10,68 +10,75 @@
 //! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError
 
 use crate::{
-  builtins::{
-      function::make_builtin_fn,
-      function::make_constructor_fn,
-      object::ObjectKind,
-      value::{ResultValue, Value},
-  },
-  exec::Interpreter,
-  profiler::BoaProfiler,
+    builtins::{
+        function::make_builtin_fn,
+        function::make_constructor_fn,
+        object::ObjectKind,
+        value::{ResultValue, Value},
+    },
+    exec::Interpreter,
+    profiler::BoaProfiler,
 };
 
 #[derive(Debug, Clone, Copy)]
 pub(crate) struct ReferenceError;
 
 impl ReferenceError {
-  /// Create a new error object.
-  pub(crate) fn make_error(this: &mut Value, args: &[Value], _: &mut Interpreter) -> ResultValue {
-      if !args.is_empty() {
-          this.set_field(
-              "message",
-              Value::from(
-                  args.get(0)
-                      .expect("failed getting error message")
-                      .to_string(),
-              ),
-          );
-      }
-      // This value is used by console.log and other routines to match Object type
-      // to its Javascript Identifier (global constructor method name)
-      this.set_kind(ObjectKind::Error);
-      Err(this.clone())
-  }
+    /// Create a new error object.
+    pub(crate) fn make_error(this: &mut Value, args: &[Value], _: &mut Interpreter) -> ResultValue {
+        if !args.is_empty() {
+            this.set_field(
+                "message",
+                Value::from(
+                    args.get(0)
+                        .expect("failed getting error message")
+                        .to_string(),
+                ),
+            );
+        }
+        // This value is used by console.log and other routines to match Object type
+        // to its Javascript Identifier (global constructor method name)
+        this.set_kind(ObjectKind::Error);
+        Err(this.clone())
+    }
 
-  /// `Error.prototype.toString()`
-  ///
-  /// The toString() method returns a string representing the specified Error object.
-  ///
-  /// More information:
-  ///  - [MDN documentation][mdn]
-  ///  - [ECMAScript reference][spec]
-  ///
-  /// [spec]: https://tc39.es/ecma262/#sec-error.prototype.tostring
-  /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/toString
-  #[allow(clippy::wrong_self_convention)]
-  pub(crate) fn to_string(this: &mut Value, _: &[Value], _: &mut Interpreter) -> ResultValue {
-      let name = this.get_field("name");
-      let message = this.get_field("message");
-      Ok(Value::from(format!("{}: {}", name, message)))
-  }
+    /// `Error.prototype.toString()`
+    ///
+    /// The toString() method returns a string representing the specified Error object.
+    ///
+    /// More information:
+    ///  - [MDN documentation][mdn]
+    ///  - [ECMAScript reference][spec]
+    ///
+    /// [spec]: https://tc39.es/ecma262/#sec-error.prototype.tostring
+    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/toString
+    #[allow(clippy::wrong_self_convention)]
+    pub(crate) fn to_string(this: &mut Value, _: &[Value], _: &mut Interpreter) -> ResultValue {
+        let name = this.get_field("name");
+        let message = this.get_field("message");
+        Ok(Value::from(format!("{}: {}", name, message)))
+    }
 
-  /// Create a new `ReferenceError` object.
-  pub(crate) fn create(global: &Value) -> Value {
-      let prototype = Value::new_object(Some(global));
-      prototype.set_field("message", Value::from(""));
+    /// Create a new `ReferenceError` object.
+    pub(crate) fn create(global: &Value) -> Value {
+        let prototype = Value::new_object(Some(global));
+        prototype.set_field("message", Value::from(""));
 
-      make_builtin_fn(Self::to_string, "toString", &prototype, 0);
+        make_builtin_fn(Self::to_string, "toString", &prototype, 0);
 
-      make_constructor_fn("ReferenceError", 1, Self::make_error, global, prototype, true)
-  }
+        make_constructor_fn(
+            "ReferenceError",
+            1,
+            Self::make_error,
+            global,
+            prototype,
+            true,
+        )
+    }
 
-  /// Initialise the global object with the `ReferenceError` object.
-  pub(crate) fn init(global: &Value) {
-      let _timer = BoaProfiler::global().start_event("referenceerror", "init");
-      global.set_field("ReferenceError", Self::create(global));
-  }
+    /// Initialise the global object with the `ReferenceError` object.
+    pub(crate) fn init(global: &Value) {
+        let _timer = BoaProfiler::global().start_event("referenceerror", "init");
+        global.set_field("ReferenceError", Self::create(global));
+    }
 }
diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index b81d2b37dca..9b5033c02a7 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -1,26 +1,21 @@
 use super::{Executable, Interpreter};
 use crate::{
-  builtins::value::{ResultValue, Value, ValueData},
-  syntax::ast::node::identifier::Identifier,
+    builtins::value::{ResultValue, Value, ValueData},
+    syntax::ast::node::identifier::Identifier,
 };
 
 impl Executable for Identifier {
-  fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
-    let reference = resolve_binding(interpreter, self.as_ref());
-    match reference.data() {
-      ValueData::Undefined => Err(
-        interpreter
-          .throw_reference_error(self.as_ref())
-          .expect_err("throw_reference_error() must return an error"),
-      ),
-      _ => Ok(reference),
+    fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
+        let reference = resolve_binding(interpreter, self.as_ref());
+        match reference.data() {
+            ValueData::Undefined => Err(interpreter
+                .throw_reference_error(self.as_ref())
+                .expect_err("throw_reference_error() must return an error")),
+            _ => Ok(reference),
+        }
     }
-  }
 }
 
 pub(crate) fn resolve_binding(interpreter: &mut Interpreter, name: &str) -> Value {
-  interpreter
-    .realm()
-    .environment
-    .get_binding_value(name)
+    interpreter.realm().environment.get_binding_value(name)
 }

From 54907c8a84d1d5e6012806aa846de37406f37e52 Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Sat, 13 Jun 2020 20:27:09 +0200
Subject: [PATCH 05/19] Temp

---
 boa/src/exec/tests.rs | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/boa/src/exec/tests.rs b/boa/src/exec/tests.rs
index e12ffca31c7..30901309cd9 100644
--- a/boa/src/exec/tests.rs
+++ b/boa/src/exec/tests.rs
@@ -63,7 +63,20 @@ fn semicolon_expression_stop() {
 fn empty_var_decl_undefined() {
     let scenario = r#"
         let b;
-        b == undefined;
+        b === undefined;
+        "#;
+
+    assert_eq!(&exec(scenario), "true");
+}
+
+#[test]
+fn identifier_on_global_object_undefined() {
+    let scenario = r#"
+        try {
+            b;
+        } catch (err) {
+            err instanceof ReferenceError;
+        }
         "#;
 
     assert_eq!(&exec(scenario), "true");

From f905f1256ec602b40c30c77861b03df28b66738d Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Sat, 13 Jun 2020 23:51:35 +0200
Subject: [PATCH 06/19] Rearange some tests

---
 boa/src/environment/lexical_environment.rs |  6 ++--
 boa/src/exec/tests.rs                      | 34 ++++++++++++++++++++--
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index 8e32c099457..a56a3c37ad1 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -290,24 +290,26 @@ mod tests {
     use crate::exec;
 
     #[test]
+    //#[ignore]
     fn let_is_blockscoped() {
         let scenario = r#"
           {
             let bar = "bar";
           }
-          bar == undefined;
+          bar;
         "#;
 
         assert_eq!(&exec(scenario), "true");
     }
 
     #[test]
+    //#[ignore]
     fn const_is_blockscoped() {
         let scenario = r#"
           {
             const bar = "bar";
           }
-          bar == undefined;
+          bar;
         "#;
 
         assert_eq!(&exec(scenario), "true");
diff --git a/boa/src/exec/tests.rs b/boa/src/exec/tests.rs
index 30901309cd9..8b80282f8d0 100644
--- a/boa/src/exec/tests.rs
+++ b/boa/src/exec/tests.rs
@@ -42,7 +42,7 @@ fn property_accessor_member_expression_bracket_notation_on_function() {
 fn empty_let_decl_undefined() {
     let scenario = r#"
         let a;
-        a == undefined;
+        a === undefined;
         "#;
 
     assert_eq!(&exec(scenario), "true");
@@ -70,6 +70,7 @@ fn empty_var_decl_undefined() {
 }
 
 #[test]
+#[ignore]
 fn identifier_on_global_object_undefined() {
     let scenario = r#"
         try {
@@ -346,7 +347,7 @@ fn do_while_post_inc() {
 }
 
 #[test]
-fn test_for_loop() {
+fn for_loop() {
     let simple = r#"
         const a = ['h', 'e', 'l', 'l', 'o'];
         let b = '';
@@ -378,7 +379,10 @@ fn test_for_loop() {
         a
         "#;
     assert_eq!(&exec(body_should_not_execute_on_false_condition), "0");
+}
 
+#[test]
+fn for_loop_iteration_variable_does_not_leak() {
     let inner_scope = r#"
         for (let i = 0;false;) {}
 
@@ -431,55 +435,79 @@ fn unary_pre() {
 }
 
 #[test]
-fn unary_typeof() {
+fn typeof_string() {
     let typeof_string = r#"
         const a = String();
         typeof a;
     "#;
     assert_eq!(&exec(typeof_string), "string");
+}
 
+#[test]
+fn typeof_int() {
     let typeof_int = r#"
         let a = 5;
         typeof a;
     "#;
     assert_eq!(&exec(typeof_int), "number");
+}
 
+#[test]
+fn typeof_rational() {
     let typeof_rational = r#"
         let a = 0.5;
         typeof a;
     "#;
     assert_eq!(&exec(typeof_rational), "number");
+}
 
+#[test]
+fn typeof_undefined() {
     let typeof_undefined = r#"
         let a = undefined;
         typeof a;
     "#;
     assert_eq!(&exec(typeof_undefined), "undefined");
+}
 
+#[test]
+fn typeof_boolean() {
     let typeof_boolean = r#"
         let a = true;
         typeof a;
     "#;
     assert_eq!(&exec(typeof_boolean), "boolean");
+}
 
+#[test]
+fn typeof_null() {
     let typeof_null = r#"
         let a = null;
         typeof a;
     "#;
     assert_eq!(&exec(typeof_null), "object");
+}
 
+#[test]
+fn typeof_object() {
     let typeof_object = r#"
         let a = {};
         typeof a;
     "#;
     assert_eq!(&exec(typeof_object), "object");
+}
 
+#[test]
+fn typeof_symbol() {
     let typeof_symbol = r#"
         let a = Symbol();
         typeof a;
     "#;
     assert_eq!(&exec(typeof_symbol), "symbol");
+}
 
+#[test]
+fn typeof_function() {
     let typeof_function = r#"
         let a = function(){};
         typeof a;

From 95cd526e1a1875bc8898dea3613566552a3a1bdb Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 12:48:12 +0200
Subject: [PATCH 07/19] Ignore some tests which are awaiting other tickets

---
 boa/src/environment/lexical_environment.rs | 8 ++++----
 boa/src/exec/tests.rs                      | 6 ++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index a56a3c37ad1..e4fa4aa98b5 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -290,7 +290,7 @@ mod tests {
     use crate::exec;
 
     #[test]
-    //#[ignore]
+    #[ignore]
     fn let_is_blockscoped() {
         let scenario = r#"
           {
@@ -298,12 +298,12 @@ mod tests {
           }
           bar;
         "#;
-
+        // awaiting agreement on error throw testing
         assert_eq!(&exec(scenario), "true");
     }
 
     #[test]
-    //#[ignore]
+    #[ignore]
     fn const_is_blockscoped() {
         let scenario = r#"
           {
@@ -311,7 +311,7 @@ mod tests {
           }
           bar;
         "#;
-
+        // awaiting agreement on error throw testing
         assert_eq!(&exec(scenario), "true");
     }
 
diff --git a/boa/src/exec/tests.rs b/boa/src/exec/tests.rs
index 8b80282f8d0..fda2d149e40 100644
--- a/boa/src/exec/tests.rs
+++ b/boa/src/exec/tests.rs
@@ -39,6 +39,7 @@ fn property_accessor_member_expression_bracket_notation_on_function() {
 }
 
 #[test]
+#[ignore] // will be solved with undefined added to global property
 fn empty_let_decl_undefined() {
     let scenario = r#"
         let a;
@@ -60,6 +61,7 @@ fn semicolon_expression_stop() {
 }
 
 #[test]
+#[ignore] // will be fixed with undefined added as global property
 fn empty_var_decl_undefined() {
     let scenario = r#"
         let b;
@@ -382,12 +384,14 @@ fn for_loop() {
 }
 
 #[test]
+#[ignore]
 fn for_loop_iteration_variable_does_not_leak() {
     let inner_scope = r#"
         for (let i = 0;false;) {}
 
         i
         "#;
+    // awaiting agreement on unhandled error handling
     assert_eq!(&exec(inner_scope), "undefined");
 }
 
@@ -462,6 +466,7 @@ fn typeof_rational() {
 }
 
 #[test]
+#[ignore] // Will be fixed when global property undefined is added
 fn typeof_undefined() {
     let typeof_undefined = r#"
         let a = undefined;
@@ -740,6 +745,7 @@ mod in_operator {
 }
 
 #[test]
+#[ignore] // maybe will be solved when undefined added to global property
 fn var_decl_hoisting() {
     let scenario = r#"
         x = 5;

From 1aeb95cacee7935bab346aec2c5dcba1697d8a86 Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 13:05:46 +0200
Subject: [PATCH 08/19] Merge resolution

---
 boa/src/builtins/error/reference.rs | 23 +++++++++++++++--------
 boa/src/builtins/mod.rs             | 27 +--------------------------
 boa/src/exec/exception.rs           | 13 -------------
 boa/src/exec/tests.rs               | 10 ----------
 4 files changed, 16 insertions(+), 57 deletions(-)

diff --git a/boa/src/builtins/error/reference.rs b/boa/src/builtins/error/reference.rs
index ff8c0aa26b5..fa59dc2d924 100644
--- a/boa/src/builtins/error/reference.rs
+++ b/boa/src/builtins/error/reference.rs
@@ -6,14 +6,14 @@
 //!  - [MDN documentation][mdn]
 //!  - [ECMAScript reference][spec]
 //!
-//! [spec]: https://tc39.es/ecma262/#sec-native-error-types-used-in-this-standard-rangeerror TODO
+//! [spec]: https://tc39.es/ecma262/#sec-native-error-types-used-in-this-standard-referenceerror
 //! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError
 
 use crate::{
     builtins::{
         function::make_builtin_fn,
         function::make_constructor_fn,
-        object::ObjectKind,
+        object::ObjectData,
         value::{ResultValue, Value},
     },
     exec::Interpreter,
@@ -24,6 +24,12 @@ use crate::{
 pub(crate) struct ReferenceError;
 
 impl ReferenceError {
+    /// The name of the object.
+    pub(crate) const NAME: &'static str = "ReferenceError";
+
+    /// The amount of arguments this function object takes.
+    pub(crate) const LENGTH: usize = 1;
+
     /// Create a new error object.
     pub(crate) fn make_error(this: &mut Value, args: &[Value], _: &mut Interpreter) -> ResultValue {
         if !args.is_empty() {
@@ -38,7 +44,7 @@ impl ReferenceError {
         }
         // This value is used by console.log and other routines to match Object type
         // to its Javascript Identifier (global constructor method name)
-        this.set_kind(ObjectKind::Error);
+        this.set_data(ObjectData::Error);
         Err(this.clone())
     }
 
@@ -67,8 +73,8 @@ impl ReferenceError {
         make_builtin_fn(Self::to_string, "toString", &prototype, 0);
 
         make_constructor_fn(
-            "ReferenceError",
-            1,
+            Self::NAME,
+            Self::LENGTH,
             Self::make_error,
             global,
             prototype,
@@ -77,8 +83,9 @@ impl ReferenceError {
     }
 
     /// Initialise the global object with the `ReferenceError` object.
-    pub(crate) fn init(global: &Value) {
-        let _timer = BoaProfiler::global().start_event("referenceerror", "init");
-        global.set_field("ReferenceError", Self::create(global));
+    pub(crate) fn init(global: &Value) -> (&str, Value) {
+        let _timer = BoaProfiler::global().start_event(Self::NAME, "init");
+
+        (Self::NAME, Self::create(global))
     }
 }
diff --git a/boa/src/builtins/mod.rs b/boa/src/builtins/mod.rs
index 80abca2abbf..72e65632dae 100644
--- a/boa/src/builtins/mod.rs
+++ b/boa/src/builtins/mod.rs
@@ -23,17 +23,12 @@ pub(crate) use self::{
     array::Array,
     bigint::BigInt,
     boolean::Boolean,
-<<<<<<< HEAD
     error::{Error, RangeError, ReferenceError, TypeError},
-    function::Function,
-=======
-    error::{Error, RangeError, TypeError},
     global_this::GlobalThis,
     infinity::Infinity,
     json::Json,
     math::Math,
     nan::NaN,
->>>>>>> master
     number::Number,
     regexp::RegExp,
     string::String,
@@ -44,25 +39,6 @@ pub(crate) use self::{
 /// Initializes builtin objects and functions
 #[inline]
 pub fn init(global: &Value) {
-<<<<<<< HEAD
-    Array::init(global);
-    BigInt::init(global);
-    Boolean::init(global);
-    json::init(global);
-    math::init(global);
-    nan::init(global);
-    Number::init(global);
-    object::init(global);
-    function::init(global);
-    RegExp::init(global);
-    String::init(global);
-    symbol::init(global);
-    console::init(global);
-    Error::init(global);
-    RangeError::init(global);
-    ReferenceError::init(global);
-    TypeError::init(global);
-=======
     let globals = vec![
         // The `Function` global must be initialized before other types.
         function::init(global),
@@ -80,7 +56,7 @@ pub fn init(global: &Value) {
         // Global error types.
         Error::init(global),
         RangeError::init(global),
-        ReferenceError::init(global);
+        ReferenceError::init(global),
         TypeError::init(global),
         // Global properties.
         NaN::init(global),
@@ -92,5 +68,4 @@ pub fn init(global: &Value) {
     for (name, value) in globals {
         global_object.insert_field(name, value);
     }
->>>>>>> master
 }
diff --git a/boa/src/exec/exception.rs b/boa/src/exec/exception.rs
index c2c8868a40e..d227662db4f 100644
--- a/boa/src/exec/exception.rs
+++ b/boa/src/exec/exception.rs
@@ -67,17 +67,4 @@ impl Interpreter {
     {
         Err(self.construct_reference_error(message))
     }
-
-    /// Throws a `Reference` with the specified message.
-    pub fn throw_reference_error<M>(&mut self, message: M) -> ResultValue
-    where
-        M: Into<String>,
-    {
-        // Runs a `new ReferenceError(message)`.
-        New::from(Call::new(
-            Identifier::from("ReferenceError"),
-            vec![Const::from(message.into()).into()],
-        ))
-        .run(self)
-    }
 }
diff --git a/boa/src/exec/tests.rs b/boa/src/exec/tests.rs
index 533469a1bc0..f52685659e3 100644
--- a/boa/src/exec/tests.rs
+++ b/boa/src/exec/tests.rs
@@ -9,16 +9,6 @@ fn function_declaration_returns_undefined() {
     assert_eq!(&exec(scenario), "undefined");
 }
 
-#[test]
-fn empty_var_decl_undefined() {
-    let scenario = r#"
-        let b;
-        b === undefined;
-        "#;
-
-    assert_eq!(&exec(scenario), "true");
-}
-
 #[test]
 fn property_accessor_member_expression_dot_notation_on_string_literal() {
     let scenario = r#"

From 3c62b33c7389dba8197c57643e08e0b04d8b6694 Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 13:31:51 +0200
Subject: [PATCH 09/19] Fix: construct_reference_error

---
 boa/src/exec/exception.rs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/boa/src/exec/exception.rs b/boa/src/exec/exception.rs
index d227662db4f..504872ed681 100644
--- a/boa/src/exec/exception.rs
+++ b/boa/src/exec/exception.rs
@@ -53,11 +53,16 @@ impl Interpreter {
     }
 
     /// Constructs a `ReferenceError` with the specified message.
-    pub fn construct_reference_error<M>(&mut self, _message: M) -> Value
+    pub fn construct_reference_error<M>(&mut self, message: M) -> Value
     where
         M: Into<String>,
     {
-        unimplemented!("ReferenceError: is not implemented");
+        New::from(Call::new(
+            Identifier::from("ReferenceError"),
+            vec![Const::from(message.into() + " is not defined").into()],
+        ))
+        .run(self)
+        .expect_err("ReferenceError should always throw")
     }
 
     /// Throws a `ReferenceError` with the specified message.

From b34da02d2a2a601effee0f9c992c8bc5b458a5e9 Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 19:45:44 +0200
Subject: [PATCH 10/19] Unignore 4 tests

---
 boa/src/environment/lexical_environment.rs | 22 +++++++++++++++-------
 boa/src/exec/tests.rs                      | 16 +++++++++-------
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index 95661eef0a8..8d339514a9c 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -290,29 +290,37 @@ mod tests {
     use crate::exec;
 
     #[test]
-    #[ignore]
     fn let_is_blockscoped() {
         let scenario = r#"
           {
             let bar = "bar";
           }
-          bar;
+
+          try{
+            bar;
+          } catch (err) {
+            err.message
+          }
         "#;
-        // awaiting agreement on error throw testing
-        assert_eq!(&exec(scenario), "true");
+
+        assert_eq!(&exec(scenario), "bar is not defined");
     }
 
     #[test]
-    #[ignore]
     fn const_is_blockscoped() {
         let scenario = r#"
           {
             const bar = "bar";
           }
-          bar;
+          
+          try{
+            bar;
+          } catch (err) {
+            err.message
+          }
         "#;
         // awaiting agreement on error throw testing
-        assert_eq!(&exec(scenario), "true");
+        assert_eq!(&exec(scenario), "bar is not defined");
     }
 
     #[test]
diff --git a/boa/src/exec/tests.rs b/boa/src/exec/tests.rs
index f52685659e3..13e636800e2 100644
--- a/boa/src/exec/tests.rs
+++ b/boa/src/exec/tests.rs
@@ -81,17 +81,16 @@ fn empty_var_decl_undefined() {
 }
 
 #[test]
-#[ignore]
 fn identifier_on_global_object_undefined() {
     let scenario = r#"
         try {
-            b;
+            bar;
         } catch (err) {
-            err instanceof ReferenceError;
+            err.message
         }
         "#;
 
-    assert_eq!(&exec(scenario), "true");
+    assert_eq!(&exec(scenario), "bar is not defined");
 }
 
 #[test]
@@ -393,15 +392,18 @@ fn for_loop() {
 }
 
 #[test]
-#[ignore]
 fn for_loop_iteration_variable_does_not_leak() {
     let inner_scope = r#"
         for (let i = 0;false;) {}
 
-        i
+        try {
+            i
+        } catch (err) {
+            err.message
+        }
         "#;
     // awaiting agreement on unhandled error handling
-    assert_eq!(&exec(inner_scope), "undefined");
+    assert_eq!(&exec(inner_scope), "i is not defined");
 }
 
 #[test]

From c810be58c64a7aa25493033a34e35c249fb250a9 Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 22:00:23 +0200
Subject: [PATCH 11/19] [undefined] add property to global scope

---
 boa/src/builtins/array/mod.rs                 |  1 +
 boa/src/builtins/mod.rs                       |  3 ++
 boa/src/builtins/undefined/mod.rs             | 32 +++++++++++++++++++
 boa/src/builtins/undefined/tests.rs           |  0
 boa/src/environment/lexical_environment.rs    |  3 +-
 boa/src/exec/identifier/mod.rs                | 16 ++++------
 boa/src/exec/mod.rs                           |  8 ++++-
 boa/src/exec/operator/mod.rs                  |  3 +-
 .../syntax/parser/expression/primary/mod.rs   |  4 +--
 9 files changed, 55 insertions(+), 15 deletions(-)
 create mode 100644 boa/src/builtins/undefined/mod.rs
 create mode 100644 boa/src/builtins/undefined/tests.rs

diff --git a/boa/src/builtins/array/mod.rs b/boa/src/builtins/array/mod.rs
index 0517e0c3ccf..d3ad4a1ecba 100644
--- a/boa/src/builtins/array/mod.rs
+++ b/boa/src/builtins/array/mod.rs
@@ -54,6 +54,7 @@ impl Array {
                 .realm()
                 .environment
                 .get_binding_value("Array")
+                .unwrap()
                 .borrow()
                 .get_field(PROTOTYPE),
         );
diff --git a/boa/src/builtins/mod.rs b/boa/src/builtins/mod.rs
index 72e65632dae..4646a3615d7 100644
--- a/boa/src/builtins/mod.rs
+++ b/boa/src/builtins/mod.rs
@@ -18,6 +18,7 @@ pub mod regexp;
 pub mod string;
 pub mod symbol;
 pub mod value;
+pub mod undefined;
 
 pub(crate) use self::{
     array::Array,
@@ -34,6 +35,7 @@ pub(crate) use self::{
     string::String,
     symbol::Symbol,
     value::{ResultValue, Value},
+    undefined::Undefined,
 };
 
 /// Initializes builtin objects and functions
@@ -62,6 +64,7 @@ pub fn init(global: &Value) {
         NaN::init(global),
         Infinity::init(global),
         GlobalThis::init(global),
+        Undefined::init(global),
     ];
 
     let mut global_object = global.as_object_mut().expect("global object");
diff --git a/boa/src/builtins/undefined/mod.rs b/boa/src/builtins/undefined/mod.rs
new file mode 100644
index 00000000000..922c284c639
--- /dev/null
+++ b/boa/src/builtins/undefined/mod.rs
@@ -0,0 +1,32 @@
+//! This module implements the global `undefined` property.
+//!
+//! The global undefined property represents the primitive value undefined.
+//!
+//! More information:
+//!  - [MDN documentation][mdn]
+//!  - [ECMAScript reference][spec]
+//!
+//! [spec]: https://tc39.es/ecma262/#sec-undefined
+//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined
+
+#[cfg(test)]
+mod tests;
+
+use crate::{builtins::value::Value, BoaProfiler};
+
+/// JavaScript global `undefined` property.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub(crate) struct Undefined;
+
+impl Undefined {
+    /// The binding name of the property.
+    pub(crate) const NAME: &'static str = "undefined";
+
+    /// Initialize the `undefined` property on the global object.
+    #[inline]
+    pub(crate) fn init(_: &Value) -> (&str, Value) {
+        let _timer = BoaProfiler::global().start_event(Self::NAME, "init");
+
+        (Self::NAME, Value::undefined())
+    }
+}
diff --git a/boa/src/builtins/undefined/tests.rs b/boa/src/builtins/undefined/tests.rs
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index 8d339514a9c..4b0450f267f 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -212,11 +212,10 @@ impl LexicalEnvironment {
             .any(|env| env.borrow().has_binding(name))
     }
 
-    pub fn get_binding_value(&self, name: &str) -> Value {
+    pub fn get_binding_value(&self, name: &str) -> Option<Value> {
         self.environments()
             .find(|env| env.borrow().has_binding(name))
             .map(|env| env.borrow().get_binding_value(name, false))
-            .unwrap_or_else(Value::undefined)
     }
 }
 
diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index 9b5033c02a7..e0f2178498a 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -1,21 +1,19 @@
 use super::{Executable, Interpreter};
 use crate::{
-    builtins::value::{ResultValue, Value, ValueData},
+    builtins::value::ResultValue,
     syntax::ast::node::identifier::Identifier,
 };
 
 impl Executable for Identifier {
     fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
-        let reference = resolve_binding(interpreter, self.as_ref());
-        match reference.data() {
-            ValueData::Undefined => Err(interpreter
+        let reference = interpreter.realm().environment.get_binding_value(self.as_ref());
+        match reference {
+            Some(value) => Ok(value),
+            None => Err(interpreter
                 .throw_reference_error(self.as_ref())
-                .expect_err("throw_reference_error() must return an error")),
-            _ => Ok(reference),
+                .expect_err("throw_reference_error() must return an error")
+            )
         }
     }
 }
 
-pub(crate) fn resolve_binding(interpreter: &mut Interpreter, name: &str) -> Value {
-    interpreter.realm().environment.get_binding_value(name)
-}
diff --git a/boa/src/exec/mod.rs b/boa/src/exec/mod.rs
index 6f97503a55f..4bdf1fb92c6 100644
--- a/boa/src/exec/mod.rs
+++ b/boa/src/exec/mod.rs
@@ -420,6 +420,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Boolean")
+                    .unwrap()
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -432,6 +433,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Number")
+                    .unwrap()
                     .get_field(PROTOTYPE);
                 Ok(Value::new_object_from_prototype(
                     proto,
@@ -443,6 +445,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Number")
+                    .unwrap()
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -455,6 +458,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("String")
+                    .unwrap()
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -467,6 +471,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Symbol")
+                    .unwrap()
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -479,6 +484,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("BigInt")
+                    .unwrap()
                     .get_field(PROTOTYPE);
                 let bigint_obj =
                     Value::new_object_from_prototype(proto, ObjectData::BigInt(bigint.clone()));
@@ -573,7 +579,7 @@ impl Executable for Node {
         let _timer = BoaProfiler::global().start_event("Executable", "exec");
         match *self {
             Node::Const(Const::Null) => Ok(Value::null()),
-            Node::Const(Const::Undefined) => Ok(Value::undefined()),
+            //Node::Const(Const::Undefined) =>  (Identifier::from((&Box::new("asd")).as_ref()).into()).run(interpreter),
             Node::Const(Const::Num(num)) => Ok(Value::rational(num)),
             Node::Const(Const::Int(num)) => Ok(Value::integer(num)),
             Node::Const(Const::BigInt(ref num)) => Ok(Value::from(num.clone())),
diff --git a/boa/src/exec/operator/mod.rs b/boa/src/exec/operator/mod.rs
index 35a099dc51b..8548b165b26 100644
--- a/boa/src/exec/operator/mod.rs
+++ b/boa/src/exec/operator/mod.rs
@@ -118,7 +118,8 @@ impl Executable for BinOp {
                     let v_a = interpreter
                         .realm()
                         .environment
-                        .get_binding_value(name.as_ref());
+                        .get_binding_value(name.as_ref())
+                        .unwrap();
                     let v_b = self.rhs().run(interpreter)?;
                     let value = Self::run_assign(op, v_a, v_b);
                     interpreter.realm.environment.set_mutable_binding(
diff --git a/boa/src/syntax/parser/expression/primary/mod.rs b/boa/src/syntax/parser/expression/primary/mod.rs
index 0e31e581cc5..43e796d74d1 100644
--- a/boa/src/syntax/parser/expression/primary/mod.rs
+++ b/boa/src/syntax/parser/expression/primary/mod.rs
@@ -86,9 +86,9 @@ impl TokenParser for PrimaryExpression {
             }
             TokenKind::BooleanLiteral(boolean) => Ok(Const::from(*boolean).into()),
             // TODO: ADD TokenKind::UndefinedLiteral
-            TokenKind::Identifier(ref i) if i.as_ref() == "undefined" => {
+            /* TokenKind::Identifier(ref i) if i.as_ref() == "undefined" => {
                 Ok(Const::Undefined.into())
-            }
+            } */
             TokenKind::NullLiteral => Ok(Const::Null.into()),
             TokenKind::Identifier(ident) => Ok(Identifier::from(ident.as_ref()).into()), // TODO: IdentifierReference
             TokenKind::StringLiteral(s) => Ok(Const::from(s.as_ref()).into()),

From ff079114c9decb250428f5db2919607cba24cba2 Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 23:02:18 +0200
Subject: [PATCH 12/19] formatting

---
 boa/src/builtins/mod.rs             |  4 ++--
 boa/src/builtins/undefined/tests.rs |  1 +
 boa/src/exec/identifier/mod.rs      | 13 ++++++-------
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/boa/src/builtins/mod.rs b/boa/src/builtins/mod.rs
index 4646a3615d7..92daa4e17f2 100644
--- a/boa/src/builtins/mod.rs
+++ b/boa/src/builtins/mod.rs
@@ -17,8 +17,8 @@ pub mod property;
 pub mod regexp;
 pub mod string;
 pub mod symbol;
-pub mod value;
 pub mod undefined;
+pub mod value;
 
 pub(crate) use self::{
     array::Array,
@@ -34,8 +34,8 @@ pub(crate) use self::{
     regexp::RegExp,
     string::String,
     symbol::Symbol,
-    value::{ResultValue, Value},
     undefined::Undefined,
+    value::{ResultValue, Value},
 };
 
 /// Initializes builtin objects and functions
diff --git a/boa/src/builtins/undefined/tests.rs b/boa/src/builtins/undefined/tests.rs
index e69de29bb2d..8b137891791 100644
--- a/boa/src/builtins/undefined/tests.rs
+++ b/boa/src/builtins/undefined/tests.rs
@@ -0,0 +1 @@
+
diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index da150ba481d..8be55d337c5 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -1,18 +1,17 @@
 use super::{Executable, Interpreter};
-use crate::{
-    builtins::value::ResultValue,
-    syntax::ast::node::identifier::Identifier,
-};
+use crate::{builtins::value::ResultValue, syntax::ast::node::identifier::Identifier};
 
 impl Executable for Identifier {
     fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
-        let reference = interpreter.realm().environment.get_binding_value(self.as_ref());
+        let reference = interpreter
+            .realm()
+            .environment
+            .get_binding_value(self.as_ref());
         match reference {
             Some(value) => Ok(value),
             None => Err(interpreter
                 .throw_reference_error(self.as_ref())
-                .expect_err("throw_reference_error() must return an error")
-            )
+                .expect_err("throw_reference_error() must return an error")),
         }
     }
 }

From e879bca1f5489447a41748465d54929e0ecadfff Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 23:10:57 +0200
Subject: [PATCH 13/19] Add couple of tests

---
 boa/src/builtins/undefined/tests.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/boa/src/builtins/undefined/tests.rs b/boa/src/builtins/undefined/tests.rs
index 8b137891791..ee8ae3394ac 100644
--- a/boa/src/builtins/undefined/tests.rs
+++ b/boa/src/builtins/undefined/tests.rs
@@ -1 +1,21 @@
 
+use crate::exec;
+
+#[test]
+fn undefined_direct_evaluation() {
+    let scenario = r#"
+        undefined;
+        "#;
+
+    assert_eq!(&exec(scenario), "undefined");
+}
+
+#[test]
+fn undefined_assignment() {
+    let scenario = r#"
+        a = undefined;
+        a
+        "#;
+
+    assert_eq!(&exec(scenario), "undefined");
+}

From d2b0ff5e1ff429342f68274e53280b5aa986b3ae Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 23:20:27 +0200
Subject: [PATCH 14/19] Tests

---
 boa/src/builtins/undefined/tests.rs        |  3 ---
 boa/src/environment/lexical_environment.rs |  2 +-
 boa/src/exec/tests.rs                      | 31 +++++++++++++++++-----
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/boa/src/builtins/undefined/tests.rs b/boa/src/builtins/undefined/tests.rs
index ee8ae3394ac..39e7cee8cee 100644
--- a/boa/src/builtins/undefined/tests.rs
+++ b/boa/src/builtins/undefined/tests.rs
@@ -1,4 +1,3 @@
-
 use crate::exec;
 
 #[test]
@@ -6,7 +5,6 @@ fn undefined_direct_evaluation() {
     let scenario = r#"
         undefined;
         "#;
-
     assert_eq!(&exec(scenario), "undefined");
 }
 
@@ -16,6 +14,5 @@ fn undefined_assignment() {
         a = undefined;
         a
         "#;
-
     assert_eq!(&exec(scenario), "undefined");
 }
diff --git a/boa/src/environment/lexical_environment.rs b/boa/src/environment/lexical_environment.rs
index 4b0450f267f..57112aa3cb3 100644
--- a/boa/src/environment/lexical_environment.rs
+++ b/boa/src/environment/lexical_environment.rs
@@ -318,7 +318,7 @@ mod tests {
             err.message
           }
         "#;
-        // awaiting agreement on error throw testing
+
         assert_eq!(&exec(scenario), "bar is not defined");
     }
 
diff --git a/boa/src/exec/tests.rs b/boa/src/exec/tests.rs
index 13e636800e2..f0b3161904d 100644
--- a/boa/src/exec/tests.rs
+++ b/boa/src/exec/tests.rs
@@ -48,7 +48,6 @@ fn property_accessor_member_expression_bracket_notation_on_function() {
 }
 
 #[test]
-#[ignore] // will be solved with undefined added to global property
 fn empty_let_decl_undefined() {
     let scenario = r#"
         let a;
@@ -70,7 +69,6 @@ fn semicolon_expression_stop() {
 }
 
 #[test]
-#[ignore] // will be fixed with undefined added as global property
 fn empty_var_decl_undefined() {
     let scenario = r#"
         let b;
@@ -402,7 +400,7 @@ fn for_loop_iteration_variable_does_not_leak() {
             err.message
         }
         "#;
-    // awaiting agreement on unhandled error handling
+
     assert_eq!(&exec(inner_scope), "i is not defined");
 }
 
@@ -477,7 +475,6 @@ fn typeof_rational() {
 }
 
 #[test]
-#[ignore] // Will be fixed when global property undefined is added
 fn typeof_undefined() {
     let typeof_undefined = r#"
         let a = undefined;
@@ -486,6 +483,14 @@ fn typeof_undefined() {
     assert_eq!(&exec(typeof_undefined), "undefined");
 }
 
+#[test]
+fn typeof_undefined_directly() {
+    let typeof_undefined = r#"
+        typeof undefined;
+    "#;
+    assert_eq!(&exec(typeof_undefined), "undefined");
+}
+
 #[test]
 fn typeof_boolean() {
     let typeof_boolean = r#"
@@ -756,8 +761,7 @@ mod in_operator {
 }
 
 #[test]
-#[ignore] // maybe will be solved when undefined added to global property
-fn var_decl_hoisting() {
+fn var_decl_hoisting_simple() {
     let scenario = r#"
         x = 5;
 
@@ -765,7 +769,10 @@ fn var_decl_hoisting() {
         x;
     "#;
     assert_eq!(&exec(scenario), "5");
+}
 
+#[test]
+fn var_decl_hoisting_with_initialization() {
     let scenario = r#"
         x = 5;
 
@@ -773,7 +780,11 @@ fn var_decl_hoisting() {
         x;
     "#;
     assert_eq!(&exec(scenario), "10");
+}
 
+#[test]
+#[ignore]
+fn var_decl_hoisting_2_variables_hoisting() {
     let scenario = r#"
         x = y;
 
@@ -783,7 +794,11 @@ fn var_decl_hoisting() {
         x;
     "#;
     assert_eq!(&exec(scenario), "10");
+}
 
+#[test]
+#[ignore]
+fn var_decl_hoisting_2_variables_hoisting_2() {
     let scenario = r#"
         var x = y;
 
@@ -791,7 +806,11 @@ fn var_decl_hoisting() {
         x;
     "#;
     assert_eq!(&exec(scenario), "undefined");
+}
 
+#[test]
+#[ignore]
+fn var_decl_hoisting_2_variables_hoisting_3() {
     let scenario = r#"
         let y = x;
         x = 5;

From e40788d59892d10d05e8c7052e084f7bec4e1e5c Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 23:24:20 +0200
Subject: [PATCH 15/19] Remove 2 comments

---
 boa/src/exec/mod.rs                             | 1 -
 boa/src/syntax/parser/expression/primary/mod.rs | 4 ----
 2 files changed, 5 deletions(-)

diff --git a/boa/src/exec/mod.rs b/boa/src/exec/mod.rs
index 4bdf1fb92c6..98e34a773cc 100644
--- a/boa/src/exec/mod.rs
+++ b/boa/src/exec/mod.rs
@@ -579,7 +579,6 @@ impl Executable for Node {
         let _timer = BoaProfiler::global().start_event("Executable", "exec");
         match *self {
             Node::Const(Const::Null) => Ok(Value::null()),
-            //Node::Const(Const::Undefined) =>  (Identifier::from((&Box::new("asd")).as_ref()).into()).run(interpreter),
             Node::Const(Const::Num(num)) => Ok(Value::rational(num)),
             Node::Const(Const::Int(num)) => Ok(Value::integer(num)),
             Node::Const(Const::BigInt(ref num)) => Ok(Value::from(num.clone())),
diff --git a/boa/src/syntax/parser/expression/primary/mod.rs b/boa/src/syntax/parser/expression/primary/mod.rs
index 43e796d74d1..5118423d56a 100644
--- a/boa/src/syntax/parser/expression/primary/mod.rs
+++ b/boa/src/syntax/parser/expression/primary/mod.rs
@@ -85,10 +85,6 @@ impl TokenParser for PrimaryExpression {
                     .into())
             }
             TokenKind::BooleanLiteral(boolean) => Ok(Const::from(*boolean).into()),
-            // TODO: ADD TokenKind::UndefinedLiteral
-            /* TokenKind::Identifier(ref i) if i.as_ref() == "undefined" => {
-                Ok(Const::Undefined.into())
-            } */
             TokenKind::NullLiteral => Ok(Const::Null.into()),
             TokenKind::Identifier(ident) => Ok(Identifier::from(ident.as_ref()).into()), // TODO: IdentifierReference
             TokenKind::StringLiteral(s) => Ok(Const::from(s.as_ref()).into()),

From ada9cc96f40825d2f5c95fb59036fbd477f4103b Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Tue, 16 Jun 2020 23:44:46 +0200
Subject: [PATCH 16/19] Replace unwrap with expect

---
 boa/src/builtins/array/mod.rs |  2 +-
 boa/src/exec/mod.rs           | 12 ++++++------
 boa/src/exec/operator/mod.rs  |  2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/boa/src/builtins/array/mod.rs b/boa/src/builtins/array/mod.rs
index d3ad4a1ecba..27c445ae069 100644
--- a/boa/src/builtins/array/mod.rs
+++ b/boa/src/builtins/array/mod.rs
@@ -54,7 +54,7 @@ impl Array {
                 .realm()
                 .environment
                 .get_binding_value("Array")
-                .unwrap()
+                .expect("Array was not initialized")
                 .borrow()
                 .get_field(PROTOTYPE),
         );
diff --git a/boa/src/exec/mod.rs b/boa/src/exec/mod.rs
index 98e34a773cc..0082422d610 100644
--- a/boa/src/exec/mod.rs
+++ b/boa/src/exec/mod.rs
@@ -420,7 +420,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Boolean")
-                    .unwrap()
+                    .expect("Boolean was not initialized")
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -433,7 +433,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Number")
-                    .unwrap()
+                    .expect("Number was not initialized")
                     .get_field(PROTOTYPE);
                 Ok(Value::new_object_from_prototype(
                     proto,
@@ -445,7 +445,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Number")
-                    .unwrap()
+                    .expect("Number was not initialized")
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -458,7 +458,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("String")
-                    .unwrap()
+                    .expect("String was not initialized")
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -471,7 +471,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("Symbol")
-                    .unwrap()
+                    .expect("Symbol was not initialized")
                     .get_field(PROTOTYPE);
 
                 Ok(Value::new_object_from_prototype(
@@ -484,7 +484,7 @@ impl Interpreter {
                     .realm
                     .environment
                     .get_binding_value("BigInt")
-                    .unwrap()
+                    .expect("BigInt was not initialized")
                     .get_field(PROTOTYPE);
                 let bigint_obj =
                     Value::new_object_from_prototype(proto, ObjectData::BigInt(bigint.clone()));
diff --git a/boa/src/exec/operator/mod.rs b/boa/src/exec/operator/mod.rs
index 8548b165b26..44d612c8c1c 100644
--- a/boa/src/exec/operator/mod.rs
+++ b/boa/src/exec/operator/mod.rs
@@ -119,7 +119,7 @@ impl Executable for BinOp {
                         .realm()
                         .environment
                         .get_binding_value(name.as_ref())
-                        .unwrap();
+                        .expect("Identifier was not initialized");
                     let v_b = self.rhs().run(interpreter)?;
                     let value = Self::run_assign(op, v_a, v_b);
                     interpreter.realm.environment.set_mutable_binding(

From 4c1e6a646c2bb4d7cd778c7bb5c272bf259ad6fc Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Wed, 17 Jun 2020 13:42:08 +0200
Subject: [PATCH 17/19] Minor - use ok_or_else instead of match construct

---
 boa/src/exec/identifier/mod.rs | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index 8be55d337c5..c2556e7f820 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -3,15 +3,14 @@ use crate::{builtins::value::ResultValue, syntax::ast::node::identifier::Identif
 
 impl Executable for Identifier {
     fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
-        let reference = interpreter
+        interpreter
             .realm()
             .environment
-            .get_binding_value(self.as_ref());
-        match reference {
-            Some(value) => Ok(value),
-            None => Err(interpreter
-                .throw_reference_error(self.as_ref())
-                .expect_err("throw_reference_error() must return an error")),
-        }
+            .get_binding_value(self.as_ref())
+            .ok_or_else(|| {
+                interpreter
+                    .throw_reference_error(self.as_ref())
+                    .expect_err("throw_reference_error() must return an error")
+            })
     }
 }

From 74974e22c4e39f8d484d944ec77264ccd3e1f4dc Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Wed, 17 Jun 2020 18:29:37 +0200
Subject: [PATCH 18/19] Cover assignmetoperator undefined case and test

---
 boa/src/exec/operator/mod.rs   |  8 +++++++-
 boa/src/exec/operator/tests.rs | 28 ++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 boa/src/exec/operator/tests.rs

diff --git a/boa/src/exec/operator/mod.rs b/boa/src/exec/operator/mod.rs
index 44d612c8c1c..f811f1737dc 100644
--- a/boa/src/exec/operator/mod.rs
+++ b/boa/src/exec/operator/mod.rs
@@ -1,4 +1,6 @@
 //! Operator execution.
+#[cfg(test)]
+mod tests;
 
 use super::{Executable, Interpreter};
 use crate::{
@@ -119,7 +121,11 @@ impl Executable for BinOp {
                         .realm()
                         .environment
                         .get_binding_value(name.as_ref())
-                        .expect("Identifier was not initialized");
+                        .ok_or_else(|| {
+                            interpreter
+                                .throw_reference_error(name.as_ref())
+                                .expect_err("throw_reference_error() must return an error")
+                        })?;
                     let v_b = self.rhs().run(interpreter)?;
                     let value = Self::run_assign(op, v_a, v_b);
                     interpreter.realm.environment.set_mutable_binding(
diff --git a/boa/src/exec/operator/tests.rs b/boa/src/exec/operator/tests.rs
new file mode 100644
index 00000000000..4d4fcbe6076
--- /dev/null
+++ b/boa/src/exec/operator/tests.rs
@@ -0,0 +1,28 @@
+use crate::exec;
+
+#[test]
+fn assignmentoperator_lhs_not_defined() {
+    let scenario = r#"
+        try {
+          a += 5
+        } catch (err) {
+          err.message
+        }
+        "#;
+
+    assert_eq!(&exec(scenario), "a is not defined");
+}
+
+#[test]
+fn assignmentoperator_rhs_throws_error() {
+    let scenario = r#"
+        try {
+          let a;
+          a += b
+        } catch (err) {
+          err.message
+        }
+        "#;
+
+    assert_eq!(&exec(scenario), "b is not defined");
+}

From 50f138118851847d3d87f846b0b53706a2a611ef Mon Sep 17 00:00:00 2001
From: croraf <vrafaeli@msn.com>
Date: Thu, 18 Jun 2020 21:02:13 +0200
Subject: [PATCH 19/19] Replace throw_reference_eror with
 construct_reference_error

---
 boa/src/exec/identifier/mod.rs | 6 +-----
 boa/src/exec/operator/mod.rs   | 6 +-----
 2 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/boa/src/exec/identifier/mod.rs b/boa/src/exec/identifier/mod.rs
index c2556e7f820..19bf6e203cb 100644
--- a/boa/src/exec/identifier/mod.rs
+++ b/boa/src/exec/identifier/mod.rs
@@ -7,10 +7,6 @@ impl Executable for Identifier {
             .realm()
             .environment
             .get_binding_value(self.as_ref())
-            .ok_or_else(|| {
-                interpreter
-                    .throw_reference_error(self.as_ref())
-                    .expect_err("throw_reference_error() must return an error")
-            })
+            .ok_or_else(|| interpreter.construct_reference_error(self.as_ref()))
     }
 }
diff --git a/boa/src/exec/operator/mod.rs b/boa/src/exec/operator/mod.rs
index f811f1737dc..86953a923e5 100644
--- a/boa/src/exec/operator/mod.rs
+++ b/boa/src/exec/operator/mod.rs
@@ -121,11 +121,7 @@ impl Executable for BinOp {
                         .realm()
                         .environment
                         .get_binding_value(name.as_ref())
-                        .ok_or_else(|| {
-                            interpreter
-                                .throw_reference_error(name.as_ref())
-                                .expect_err("throw_reference_error() must return an error")
-                        })?;
+                        .ok_or_else(|| interpreter.construct_reference_error(name.as_ref()))?;
                     let v_b = self.rhs().run(interpreter)?;
                     let value = Self::run_assign(op, v_a, v_b);
                     interpreter.realm.environment.set_mutable_binding(