JS: add test for DOM access where expression appears to have no side effects

Author: Napalys

javascript/ql/test/query-tests/Expressions/ExprHasNoEffect/ExprHasNoEffect.expected

@@ -1,3 +1,11 @@
+| dom.js:2:5:2:30 | a.clien ... ientTop | This expression has no effect. |
+| dom.js:2:5:2:50 | a.clien ...  === !0 | This expression has no effect. |
+| dom.js:2:33:2:50 | a.clientTop === !0 | This expression has no effect. |
+| dom.js:3:5:3:20 | a && a.clientTop | This expression has no effect. |
+| dom.js:4:5:4:28 | a.clien ... ientTop | This expression has no effect. |
+| dom.js:5:18:5:43 | a.clien ... ientTop | This expression has no effect. |
+| dom.js:6:18:6:63 | b && (b ... entTop) | This expression has no effect. |
+| dom.js:6:23:6:63 | (b.clie ... entTop) | This expression has no effect. |
 | try.js:22:9:22:26 | x.ordinaryProperty | This expression has no effect. |
 | tst2.js:2:4:2:4 | 0 | This expression has no effect. |
 | tst.js:3:1:3:2 | 23 | This expression has no effect. |

javascript/ql/test/query-tests/Expressions/ExprHasNoEffect/dom.js

@@ -0,0 +1,7 @@
+function f(){
+    a.clientTop && a.clientTop, a.clientTop === !0; // $Alert
+    a && a.clientTop; // $SPURIOUS:Alert
+    a.clientTop, a.clientTop; // $SPURIOUS:Alert
+    if(a) return a.clientTop && a.clientTop, a.clientTop === !0 // $SPURIOUS:Alert
+    if(b) return b && (b.clientTop, b.clientTop && b.clientTop), null // $SPURIOUS:Alert
+}