1. ECMAScript 5

    Full support for the ECMAScript 5 specification. Features include `Function.prototype.bind`, Array methods like `indexOf`, `forEach`, `map` & `filter`, Object methods like `defineProperty`, `create` & `keys`, the `trim` method on Strings and many more.

  2. Form validation

    Method of setting required fields and field types without requiring JavaScript. This includes preventing forms from being submitted when appropriate, the `checkValidity()` method as well as support for the `:invalid`, `:valid`, and `:required` CSS pseudo-classes.

  3. sandbox attribute for iframes

    Method of running external site pages with reduced privileges (e.g. no JavaScript) in iframes.

  4. requestIdleCallback

    API allowing the execution of JavaScript to be queued to run in idle browser time, either at the end of a frame or when the user is inactive. Also covers support for `cancelIdleCallback`. The API has similarities with `requestAnimationFrame`.

  5. javascript built-in: intl: datetimeformat: supportedlocalesof

  6. javascript built-in: intl: listformat: supportedlocalesof

  7. javascript built-in: intl: numberformat: supportedlocalesof

  8. javascript built-in: intl: relativetimeformat: supportedlocalesof

  9. javascript statement: `for await...of`

  10. javascript statement: `for...of`

  11. javascript statement: `for...of`: closing iterators