Additions and Changes That Introduce Incompatibilities with Prior Editions
- : In ECMAScript 2015, ToNumber applied to a String value now recognizes and converts |BinaryIntegerLiteral| and |OctalIntegerLiteral| numeric strings. In previous editions such strings were converted to *NaN*.
: In ECMAScript 2015, Function calls are not allowed to return a Reference value.
+ : In ECMAScript 2015, ToNumber applied to a String value now recognizes and converts |BinaryIntegerLiteral| and |OctalIntegerLiteral| numeric strings. In previous editions such strings were converted to *NaN*.
+ : In ECMAScript 2018, Template objects are canonicalized based on Parse Node (source location), instead of across all occurrences of that template literal or tagged template in a Realm in previous editions.
+ : In ECMASCript 2016, Unicode 8.0.0 or higher is mandated, as opposed to ECMAScript 2015 which mandated Unicode 5.1. In particular, this caused U+180E MONGOLIAN VOWEL SEPARATOR, which was in the `Space_Separator` (`Zs`) category and thus treated as whitespace in ECMAScript 2015, to be moved to the `Format` (`Cf`) category (as of Unicode 6.3.0). This causes whitespace-sensitive methods to behave differently. For example, `"\u180E".trim().length` was `0` in previous editions, but `1` in ECMAScript 2016 and later. Additionally, ECMAScript 2017 mandated always using the latest version of the Unicode standard.
: In ECMAScript 2015, the valid code points for an |IdentifierName| are specified in terms of the Unicode properties “ID_Start” and “ID_Continue”. In previous editions, the valid |IdentifierName| or |Identifier| code points were specified by enumerating various Unicode code point categories.
: In ECMAScript 2015, Automatic Semicolon Insertion adds a semicolon at the end of a do-while statement if the semicolon is missing. This change aligns the specification with the actual behaviour of most existing implementations.
: In ECMAScript 2015, it is no longer an early error to have duplicate property names in Object Initializers.
@@ -42836,6 +42838,8 @@ Additions and Changes That Introduce Incompatibilities with Prior Editions In ECMAScript 2015, If the _pattern_ argument is a RegExp instance and the _flags_ argument is not *undefined*, a new RegExp instance is created just like _pattern_ except that _pattern_'s flags are replaced by the argument _flags_. In previous editions a *TypeError* exception was thrown when _pattern_ was a RegExp instance and _flags_ was not *undefined*.
In ECMAScript 2015, the RegExp prototype object is not a RegExp instance. In previous editions it was a RegExp instance whose pattern is the empty string.
In ECMAScript 2015, `"source"`, `"global"`, `"ignoreCase"`, and `"multiline"` are accessor properties defined on the RegExp prototype object. In previous editions they were data properties defined on RegExp instances.
+ : In ECMAScript 2019, `Atomics.wake` has been renamed to `Atomics.notify` to prevent confusion with `Atomics.wait`.
+ , : In ECMAScript 2019, the number of Jobs enqueued by `await` was reduced, which could create an observable difference in resolution order between a `then()` call and an `await` expression.