test(Date): JSDate.WtF (#21)

Questions 1-7 / 28

Author: percebus

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,11 +1,13 @@
-# Summary
+# Change
 
-{FIXME}
+## Issues
+
+- #{FIXME}
 
-# Details
+## Summary
 
 {FIXME}
 
-# Changes in action
+## Changes in action
 
 {FIXME}

README.md

@@ -39,3 +39,8 @@ $> npm run testem:ci
 ### Kyle Simpsons
 
 See his [What the... JavaScript?](https://www.youtube.com/watch?v=2pL28CcEijU) lecture, from [forwardJS.com](http://forwardjs.com/)
+
+## References
+
+- [`new Date("wtf")`](https://jsdate.wtf/)
+  - [*"I hate JavaScript"*, Theo - t3.gg](https://www.youtube.com/watch?v=7bvBVBy_CrM)

__tests__/Date/wtf.unit.spec.js

@@ -0,0 +1,131 @@
+// SRC: https://jsdate.wtf/
+describe('Date', () => {
+  let oDate, dateString, dateValue, milliseconds
+
+  // 1 of 28
+  describe('new Date("0")', () => {
+    beforeEach(() => {
+      oDate = new Date('0')
+      dateString = oDate.toISOString()
+    })
+
+    it('does NOT equal "1970-01-01T00:00:00.000Z"', () => {
+      expect(dateString).not.toEqual('1970-01-01T00:00:00.000Z')
+    })
+
+    // FIXME? it matches in CI, but not in my local.
+    // Is it because I am on GMT-6?
+    // The string "0" is interpreted as the year 2000, not as a timestamp!
+    xit('interprets "0" as the year 2000, not as a timestamp!', () => {
+      expect(dateString).not.toEqual('2000-01-01T00:00:00.000Z') // According to https://jsdate.wtf
+      expect(dateString).toEqual('2000-01-01T06:00:00.000Z')
+    })
+  })
+
+  // 2 of 28
+  describe('new Date(0)', () => {
+    beforeEach(() => {
+      oDate = new Date(0)
+      dateString = oDate.toISOString()
+    })
+
+    it('does NOT equal "2000-01-01T00:00:00.000Z"', () => {
+      expect(dateString).not.toEqual('2000-01-01T00:00:00.000Z')
+    })
+
+    // The number 0, as opposed to the string "0",
+    // is interpreted as milliseconds since the Unix epoch (Jan 1, 1970).
+    it('interprets 0 as a timestamp', () => {
+      expect(dateString).toEqual('1970-01-01T00:00:00.000Z')
+    })
+  })
+
+  // 3 of 28
+  describe('Date.parse(0) === Date.parse("0")', () => {
+    // Both parse to 946684800000 milliseconds!
+    // Date.parse only operates on strings,
+    // so 0 is coerced to the string "0".
+    it('is true', () => {
+      const firstDate = Date.parse(0)
+      const secondDate = Date.parse('0')
+
+      expect(firstDate === secondDate).not.toBe(false)
+      expect(firstDate === secondDate).toBe(true)
+    })
+  })
+
+  // 4 of 28
+  describe('new Date("not a date")', () => {
+    beforeEach(() => {
+      oDate = new Date('not a date')
+      dateValue = oDate.valueOf()
+    })
+
+    it('is NOT null', () => {
+      expect(oDate).not.toBe(null)
+    })
+
+    it('is NOT undefined', () => {
+      expect(oDate).not.toBe(undefined)
+    })
+
+    // Invalid Date is still a Date object!
+    // It's not null or an error.
+    it('is Invalid Date', () => {
+      expect(Number.isNaN(dateValue)).not.toBe(false)
+      expect(Number.isNaN(dateValue)).toBe(true)
+      expect(dateValue).toBeNaN()
+    })
+
+    // 5 of 28
+    describe('.getTime()', () => {
+      beforeEach(() => {
+        milliseconds = oDate.getTime()
+      })
+
+      it('is NOT null', () => {
+        expect(milliseconds).not.toBe(null)
+      })
+
+      it('is NOT 0', () => {
+        expect(milliseconds).not.toBe(0)
+      })
+
+      // Invalid Date objects return NaN for getTime().
+      // This function returns the number of milliseconds since the Unix epoch for valid dates.
+      it('is NaN', () => {
+        expect(Number.isNaN(milliseconds)).not.toBe(false)
+        expect(Number.isNaN(milliseconds)).toBe(true)
+        expect(milliseconds).toBeNaN()
+      })
+    })
+
+    // 6 of 28
+    describe('.toISOString()', () => {
+      // toISOString() throws a RangeError on Invalid Date objects.
+      it('throws an error', () => {
+        expect(() => oDate.toISOString()).toThrow()
+      })
+    })
+
+    // 7 of 28
+    describe('.toTimeString()', () => {
+      beforeEach(() => {
+        dateString = oDate.toTimeString()
+      })
+
+      it('does NOT equal ""', () => {
+        expect(dateString).not.toEqual('')
+      })
+
+      it('is NOT null', () => {
+        expect(dateString).not.toBe(null)
+      })
+
+      // toTimeString() returns the string "Invalid Date" for invalid dates. 🫠
+      it('equals "Invalid Date"', () => {
+        expect(dateString).toEqual('Invalid Date')
+      })
+    })
+  })
+})