New Features in JavaScript 2018

New RegExp Features in 2018

Browser Support

ECMAScript 2018 is supported in all modern browsers since Jun 2020:

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 Promise.finally()

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

Promise.finally() defines a function to be executed when a promise has either been successfully resolved rejected.

Example

let myPromise = new Promise();

myPromise.then();

myPromise.catch();

myPromise.finally();

JavaScript Array Rest Elements

ECMAScript 2018 added the rest operator (...).

The rest operator (...) allows us to destruct an array and collect the leftovers:

Example 1

let a, rest;

const arr1 = [1,2,3,4,5,6,7,8];

[a, ...rest] = arr1;

Example 2

let a, b, rest;

const arr1 = [1,2,3,4,5,6,7,8];

[a, b, ...rest] = arr1;

JavaScript Object Rest Properties

ECMAScript 2018 added the rest operator (...).

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

Example

// Create an Object:

const car = {type:"Fiat", model:"500", color:"white"};

// Destructure the Object

let {type, model, color} = car;

document.getElementById("demo").innerHTML = "The car type is: " + type;

New JavaScript RegExp Features

ECMAScript 2018 added 4 new RegExp features:

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

RegExp /s Flag

Example

let text = "Line\nLine.";

let pattern = /Line./gs;

let result = text.match(pattern);

Description

The s (dotAll) flag allows the . (dot) metacharacter to match any character, including line terminator characters (like \n, \r, \u2028, \u2029).

Without s, \n does not match line terminators.

RegExp \p Metacharacter

Example

let text = "Hello 😄";

let pattern = /\p{RGI_Emoji}/v;

let result = pattern.test(text);

Description

The \p{Unicode Property} metacharacter matches any character with a Unicode character property.

RegExp Lookbehind

Example (?<=y)x

let text = "Hello W3Schools";

let pattern = /(?<=Hello )W3Schools/;

let result = pattern.test(text);

Description

(?<=y)x matches "x" if "x" is preceded by "y".

Negative Lookbehind

Example (?<!y)x

let text = "Hello W3Schools";

let pattern = /(?<=Hello )W3Schools/;

let result = pattern.test(text);

Description

(?<!y)x matches "x" if "x" is NOT preceded by "y".

RegExp Named Capturing Groups

Example (?...)

const text = "Name: John Doe";

// Using named capturing groups

const regex = /(?<firstName>\w+) (?<lastName>\w+)/;

const match = text.match(regex);

let fName = match.groups.firstName;

let lName = match.groups.lastName;

Explained

• (?\w+) captures a word and labels it firstName
• (?\w+) does the same for lastName
• text.match() returns an array with a groups property
• match.groups() returns an object: {firstName:"John", lastName:"Doe" }

When using a regular expression with capturing groups, the match() method of a string returns a result array that includes a groups property. This groups property is an object that holds the matches for named capturing groups.

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.