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JavaScript ECMAScript 2018

Original JavaScript version numbers were ES5 (2009) and ES6 (2015)

New Features in ECMAScript 2018

This chapter introduces the new features in ECMAScript 2018:

  • Asynchronous Iteration
  • Promise Finally
  • Object Rest Properties
  • New RegExp Features

    • JavaScript Asynchronous Iteration

    ECMAScript 2018 added asynchronous iterators and iterables.

    With asynchronous iterables, we can use the await keyword in for/of loops.

    Example

    for await () {}

    Firefox and Safari were the first browsers with support for JavaScript asynchronous iteration:

    Chrome 63 Edge 79 Firefox 57 Safari 11 Opera 50
    Dec 2017 Jan 2020 Nov 2017 Sep 2017 Jan 2018

    JavaScript Promise.finally

    ECMAScript 2018 finalizes the full implementation of the Promise object with Promise.finally:

    Example

    let myPromise = new Promise();

    myPromise.then();
    myPromise.catch();
    myPromise.finally();

    Chrome and Firefox were the first browsers with support for Promise.finally:

    Chrome 63 Edge 18 Firefox 58 Safari 11.1 Opera 50
    Dec 2017 Nov 2018 Jan 2018 Mar 2018 Jan 2018

    JavaScript Object Rest Properties

    ECMAScript 2018 added rest properties.

    This allows us to destruct an object and collect the leftovers onto a new object:

    Example

    let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
    x; // 1
    y; // 2
    z; // { a: 3, b: 4 }

    Chrome, Firefox, ans Opera were the first browsers with support for object rest properties:

    Chrome 60 Edge 79 Firefox 55 Safari 11.1 Opera 47
    Jul 2017 Jan 2020 Aug 2017 Mar 2018 Aug 2017

    New JavaScript RegExp Features

    ECMAScript 2018 added 4 new RegExp features:

  • Unicode Property Escapes (\p{...})
  • Lookbehind Assertions (?<= ) and (?<! )
  • Named Capture Groups
  • s (dotAll) Flag

    • Chrome and Firefox were the first browsers with support for all the new RegExp features:

    Chrome 64 Edge 79 Firefox 78 Safari 12 Opera 51
    Jan 2018 Jan 2020 Jun 2020 Sep 2018 Feb 2018

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