JavaScript Version Numbers

Old ECMAScript versions was named by numbers: ES5 and ES6.

From 2016, versions are named by year: ES2016, 2018, 2020 ...

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 Shared Memory

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 () {}

JavaScript asynchronous iteration is supported in all modern browsers since January 2020:

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();

Promise.finally is supported in all modern browsers since November 2018:

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 }

Object rest properties is supported in all modern browsers since January 2020:

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

The new RegExp features is supported in all modern browsers since June 2020:

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

JavaScript Threads

In JavaScript you use the Web Workers API to create threads.

Worker threads are used to execute code in the background so that the main program can continue execution.

Worker threads run simultaneously with the main program. Simultaneous execution of different parts of a program can be time-saving.

JavaScript Shared Memory

Shared memory is a feature that allows threads (different parts of a program) to access and update the same data in the same memory.

Instead of passing data between threads, you can pass a SharedArrayBuffer object that points to the memory where data is saved.

SharedArrayBuffer

A SharedArrayBuffer object represents a fixed-length raw binary data buffer similar to the ArrayBuffer object.