ECMAScript 2023 officially released

ECMAScript 2023 has now been approved by ECMA International . ECMAScript, the standardized JavaScript language, was first published in 1997 and has grown to become one of the most widely used general-purpose programming languages in the world.

This Ecma standard defines the ECMAScript 2023 Language, the 14th edition of the ECMAScript language specification.

ECMAScript 2023, 14th edition, introduces the , , , and methods on Array.prototypeand above ; adds support for comments at the beginning of files to better facilitate the executable of ECMAScript files; and allows Use most Symbols as keys.TypedArray.prototypetoSortedtoReversedwithfindLastfindLastIndexArray.prototypetoSpliced#!

The final proposal, published on GitHub by ECMA TC39, details four features that will be released this year:

Array find from last

This proposal adds and methods to the Arrayand prototype . This is the same behavior as Array.prototype.find and Array.prototype.findIndex , but will iterate from the last to the firstTypedArrayfindLast()findLastIndex()

const array = [{ value: 1 }, { value: 2 }, { value: 3 }, { value: 4 }];

array.find(n => n.value % 2 === 1); // { value: 1 }
array.findIndex(n => n.value % 2 === 1); // 0

// ======== Before the proposal =========== 

// find
[...array].reverse().find(n => n.value % 2 === 1); // { value: 3 }

// findIndex
array.length - 1 - [...array].reverse().findIndex(n => n.value % 2 === 1); // 2
array.length - 1 - [...array].reverse().findIndex(n => n.value === 42); // should be -1, but 4

// ======== In the proposal =========== 
// find
array.findLast(n => n.value % 2 === 1); // { value: 3 }

// findIndex
array.findLastIndex(n => n.value % 2 === 1); // 2
array.findLastIndex(n => n.value === 42); // -1

Hashbang Grammar

A hashbang, also known as a shebang, is a sequence of characters at the beginning of an executable script that defines the program's interpreter to run. When the Unix kernel's program loader executes a JavaScript program, the host strips off the hashbang to generate valid source before passing it to the engine. The Hashbang Grammar proposal standardizes how this is done.

#!/usr/bin/env node
// in the Script Goal
'use strict';
console.log(1);

#!/usr/bin/env node
// in the Module Goal
export {};
console.log(1);

Symbols as WeakMap keys

This proposal extends the WeakMap API to allow the use of unique Symbols as keys.

const weak = new WeakMap();

// Pun not intended: being a symbol makes it become a more symbolic key
const key = Symbol('my ref');
const someObject = { /* data data data */ };

weak.set(key, someObject);

Change Array by Copy

Additional methods are provided on and that implement mutations to an array by returning a new copy with the mutations Array.prototype.TypedArray.prototype

const sequence = [1, 2, 3];
sequence.toReversed(); // => [3, 2, 1]
sequence; // => [1, 2, 3]

const outOfOrder = new Uint8Array([3, 1, 2]);
outOfOrder.toSorted(); // => Uint8Array [1, 2, 3]
outOfOrder; // => Uint8Array [3, 1, 2]

const correctionNeeded = [1, 1, 3];
correctionNeeded.with(1, 2); // => [1, 2, 3]
correctionNeeded; // => [1, 1, 3]

For details, you can view:

ECMAScript 2023 officially released

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