【待翻译】What's New in ECMAScript 2020 (ES11)

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翻译: EN
目录

The latest draft of ECMAScript 2020 was release on November 27 2019. All proposals in Stage 4 are included in this version of the language.

Let’s take a brief look at what new features are brought into ES11.

  • String.prototype.matchAll
  • Dynamic import()
  • BigInt
  • Promise.allSettled
  • globalThis

String.prototype.matchAll

The matchAll() method returns an iterator of all results matching a string against a regular expression, including capturing groups.

let regexp = /t(e)(st(\d?))/g;
let str = 'test1test2';

let array = [...str.matchAll(regexp)];

console.log(array[0]);
// expected output: Array ["test1", "e", "st1", "1"]

console.log(array[1]);
// expected output: Array ["test2", "e", "st2", "2"]

Dynamic import()

import() accepts an arbitrary string (not just string literals), and returns a Promise.

let moduleName = getModuleName()
import(`./section-modules/${moduleName}.js`)
  .then(module => {
    module.loadPageInto(main);
  })
  .catch(err => {
    main.textContent = err.message;
  });

Read Specification

BigInt

BigInt is a new primitive that provides a way to represent whole numbers larger than 253, which is the largest number Javascript can reliably represent with the Number primitive. A BigInt is created by appending n to the end of the integer or by calling the constructor.

const x = Number.MAX_SAFE_INTEGER;
// ↪ 9007199254740991, this is 1 less than 2^53

const y = x + 1;
// ↪ 9007199254740992, ok, checks out

const z = x + 2
// ↪ 9007199254740992, wait, that’s the same as above!


// BigInt
const theBiggestInt = 9007199254740991n;

const alsoHuge = BigInt(9007199254740991);
// ↪ 9007199254740991n

const hugeButString = BigInt('9007199254740991');
// ↪ 9007199254740991n

Promise.allSettled

The Promise.allSettled() method returns a promise that resolves after all of the given promises have either resolved or rejected, with an array of objects that each describes the outcome of each promise.

const promise1 = Promise.resolve(3);
const promise2 = new Promise((resolve, reject) => setTimeout(reject, 100, 'foo'));
const promises = [promise1, promise2];

Promise.allSettled(promises).
  then((results) => results.forEach((result) => console.log(result.status)));

// expected output:
// "fulfilled"
// "rejected"

There is another proposal Promise.any which has been in Stage 3.

See also Promise.all and Promise.race

globalThis

Prior to globalThis, the only reliable cross-platform way to get the global object for an environment was Function('return this')(). However, this causes CSP violations in some settings.

Read globalThis Specification