We recently shipped import maps in Firefox 108 and this article is the first in a series that describes what they are and the problems they can solve. In this first article, we will go through the background and basics of import maps and follow up with a second article explaining more details of import maps. Background: JavaScript Modules If you don’t know JavaScript modules, you can read the MDN
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GitHub - tc39/proposal-error-cause: TC39 proposal for accumulating errors
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GitHub - tc39/proposal-regexp-v-flag: UTS18 set notation in regular expressions
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This post is for people who are familiar with JavaScript’s == operator. JavaScript’s “double equals” operator, ==, is typically discouraged. And for good reason: its behavior is tricky. Where === asks “are these the same thing?”, the double-equals operator asks a question that’s not straightforward. More specifically, == implements something called the Abstract Equality Comparison Algorithm, a 13-
GitHub - tc39/proposal-string-dedent: TC39 Proposal to remove common leading indentation from multiline template strings
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Official name bikeshed · Issue #321 · tc39/proposal-shadowrealm
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Annex B について JavaScript の言語仕様には Annex B という項目があります。ここには Web 互換性のために残されているレガシーな機能の仕様について記述してあり、新たに ECMAScript のコードを書く際にこれらの機能を使用したり、その存在を前提にしたりしてはいけないと明記されています。 String#big などの今となっては全く実用性のないメソッドや、escape, unescape 函数、もともと IE の独自実装だった String#substr などについて記述されています。 ブラウザではこれらの機能を取り除くことが出来ないので残念ながら扱うことが出来ます。また Chrome の JavaScript エンジンである V8 を使っている Node.js や Deno でも Web 互換性を重視していることもあって扱うことが出来ます。 一方で Web
Theme 第 78 回のテーマは TC39 です。 今回は Prettier のメンテなや Babel のコントリビュータをやりながら、 TC39 の新しいプロポーサルをそれらに実装する作業をしている @__sosukesuzuki をゲストにお呼びし、 Prettier/Babel のメンテナンスの話などを交え、 TC39 のウォッチの仕方や、気になる Proposal の話、 ES2021 の展望を議論しながら、今後の ES や TC39 について議論しました。 Show Note Prettier - Opinionated Code Formatter Babel - The compiler for next generation JavaScript Web 技術の調査方法 | blog.jxck.io TC39 tc39/proposals tc39/agendas tc3
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GitHub - wessberg/cjstoesm: A tool that can transform CommonJS to ESM
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【2024/10/08】 Stage 4 となり、ES2025 に入ることが確定したため、タイトルと本文を更新 TypeScript 5.6 がリリースされたため、Beta の記述を消去 【2024/08/11】 TypeScript の BuiltinIterator が IteratorObject にリネームされたため修正 【2024/07/28】 TypeScript 5.6 Beta より Iterator Helpers の型サポート BuiltinIterator が入るため、その章を追加 【2023/10/01】 2023年1月に Async Iterator Helpers が別の提案としてスプリットされ Stage 2 に降格されたため、一部内容を変更 【2022/12/02】 2022年11月に Stage 3 になったため記事のタイトル、一部内容を変更 イテレーター
TC39 の 86 回目のミーティングが 10/25 ~ 10/28 に開催されました。 このミーティングで議題に上がった提案と、そのステージの移動について紹介します。 agendas/10.md at master · tc39/agendas Oct 2021 · Issue #77 · babel/proposals for Stage 4 Error Cause Stage 4 になりました。ECMAScript 2022 に入ります Error Cause は、Error コンストラクタの第 2 引数に cause という値で原因となったエラーを渡すことができるようにする提案です。 キャッチする側では、error.cause で、そのエラーを取得できます。 例を示します。 doUploadJob 関数は fetch を実行して失敗したときに新しいエラーをスローします。そのエラーの
GitHub - tc39/proposal-structs: JavaScript Structs: Fixed Layout Objects
Structs are declarative sealed objects. There are two kinds of structs: unshared structs and shared structs. Unshared structs behave as if they were sealed objects. Shared structs have additional restrictions and can be concurrently accessed from different agents. Both unshared and shared structs have the following properties: Opaque storage like plain objects. Not aliasable via ArrayBuffer or Sha
Node Modules at War: Why CommonJS and ES Modules Can’t Get Along
Dan Fabulich is a Principal Engineer at Redfin. (We’re hiring!) In Node 14, there are now two kinds of scripts: there are old-style CommonJS (CJS) scripts and new-style ESM scripts (aka MJS). CJS scripts use require() and module.exports; ESM scripts use import and export. ESM and CJS are completely different animals. Superficially, ESM looks very similar to CJS, but their implementations couldn’t
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ECMAScript仕様書を 誰でも読めるようにする 技術を求めて yebis0942 JSConf.jp 2022
This release doesn't contain any deliberately-breaking changes. However, it contains a very complex new feature and while all of esbuild's tests pass, I would not be surprised if an important edge case turns out to be broken. So I'm releasing this as a breaking change release to avoid causing any trouble. As usual, make sure to test your code when you upgrade. Implement the JavaScript decorators p
GitHub - tc39/ecma426: Source map specification, RFCs and new proposals.
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Package exports | webpack
The exports field in the package.json of a package allows to declare which module should be used when using module requests like import "package" or import "package/sub/path". It replaces the default implementation that returns main field resp. index.js files for "package" and the file system lookup for "package/sub/path". When the exports field is specified, only these module requests are availab
GitHub - tc39/proposal-array-grouping: A proposal to make grouping of array items easier
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ECMAScript proposal: JSON modules
In this blog post, we examine the ECMAScript proposal “JSON modules” (by Sven Sauleau, Daniel Ehrenberg, Myles Borins, and Dan Clark). It lets us import JSON data as if it were an ECMAScript module. Why would we want to import JSON like a module? # Various bundlers (such as webpack) have allowed us to import JSON data as if it were an ECMAScript module for a long time. JSON modules turn this into
Ecma International approves ECMAScript 2024: What’s new? On 26 June 2024, the 127th Ecma General Assembly approved the ECMAScript 2024 language specification (press release, GitHub release), which means that it’s officially a standard now. This blog post explains what’s new. The editors of ECMAScript 2024 # The editors of this release are: Shu-yu Guo Michael Ficarra Kevin Gibbons What’s new in EC
GitHub - tc39/proposal-decimal: Built-in exact decimal numbers for JavaScript
Accurate storage and processing of base-10 decimal numbers is a frequent need in JavaScript. Currently, developers sometimes represent these using libraries for this purpose, or sometimes use Strings. Sadly, JavaScript Numbers are also sometimes used, leading to real, end-user-visible rounding errors. What’s the issue? Why aren’t JS Numbers good enough? In what sense are they not “exact”? How is i
Release 3.0.0: ECMAScript 2021対応 · asciidwango/js-primer
JavaScript Primerのウェブ版がECMAScript 2021に対応しました 🎉 JavaScript Primerのウェブサイトから閲覧できます。 ウェブサイト: https://jsprimer.net/ 対応のサマリIssue: ES2021の対応 · Issue #1220 · asciidwango/js-primer 昨年のES2020のリリースノート: Release 2.0.0: ECMAScript 2020対応 JavaScript Primerについて JavaScript Primerは、これからJavaScriptを学びたい人が、ECMAScript 2015以降をベースにして一からJavaScriptを学べる書籍です。 ECMAScriptの仕様は毎年アップデートされるため、JavaScript Primerも毎年それに対応できるように継続してア
In this TC39 meeting, the updates to JavaScript Classes around private state have moved to stage 4. Other proposals of note this meeting were proposals related to ArrayBuffers, notably resizable ArrayBuffers and a new proposal, introducing read-only ArrayBuffers and fixed views into ArrayBuffers. Read-only ArrayBuffers are not a new ArrayBuffer, but rather a way to freeze existing ArrayBuffers so
Ecma International approves ECMAScript 2022: What’s new? On 22 June 2022, the 123nd Ecma General Assembly approved the ECMAScript 2022 language specification, which means that it’s officially a standard now. This blog post explains what’s new. The editors of ECMAScript 2022 # The editors of this release are: Shu-yu Guo Michael Ficarra Kevin Gibbons What’s new in ECMAScript 2022? # New members of
Temporal API is Awesome · Taro
Wednesday, August 23, 2023 Dates in JS suck. Well, they suck in all languages, really. It's surprisingly hard to get right. The native Date is super limited. Sure, you can new Date('2015-10-21T01:22:00.000Z') and date.toISOString(), maybe dateA < dateB, but that's pretty much it. Need to add minutes, hours, or whatever to a date, check how many days there are until X date, etc? Good luck with that
The ECMAScript proposal “Import assertions” (by Myles Borins, Sven Sauleau, Dan Clark, and Daniel Ehrenberg) introduces syntax for associating metadata with import statements. In this blog post, we examine what that looks like and why it’s useful. Import assertions # The motivating use case for import assertions was importing JSON data as a module. That looks as follows (and is further specified
GitHub - es-meta/esmeta: ECMAScript Specification (ECMA-262) Metalanguage
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The triple dot syntax (...) in JavaScript: rest vs. spread In JavaScript, the same syntax – triple dots (...) – is used for two different mechanisms: Rest syntax is for receiving data. Spreading is for sending data. This blog post examines how these mechanisms work and why they are not operators. Receiving data: rest syntax # A rest parameter is a special kind of parameter that receives all remai
ES2021 features list
ES2021 Features! Logical Assignment Operators (&&= ||= ??=) Numeric Separators (1_000) Promise.any & AggregateError String.prototype.replaceAll WeakRefs & FinalizationRegistry Objects Logical Assignment Operators Logical Assignment Operators 📖. //"Or Or Equals" x ||= y; x || (x = y); // "And And Equals" x &&= y; x && (x = y); // "QQ Equals" x ??= y; x ?? (x = y);const updateID = user => { // We c
ES2023 features list
ES2023 Features! Array find from last Hashbang Grammar Symbols as WeakMap keys Change array by copy Array find from last Array.prototype.findLast and Array.prototype.findLastIndex 📕 let nums = [5,4,3,2,1]; let lastEven = nums.findLast((num) => num % 2 === 0); // 2 let lastEvenIndex = nums.findLastIndex((num) => num % 2 === 0); // 3Hashbang Grammar #! for JS 📕 The first line of this script begins
(遍歴) 初めて触った JavaScript は ES5 で、Vue, Reactから入り、jQueryはほとんどやらずに生きてきました
GitHub - antfu/esbuild-node-loader: Transpile TypeScript to ESM with Node.js loader.
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After reading notes from the last TC39 meeting, it looks like the list of new features coming to JavaScript is already known. The final version of the ECMAScript specification is expected to be published at the end of June. Last and most important thing is that we are cutting ES2023. We are freezing it, or rather we have frozen it, I should say. We are not expecting any more significant editorial
At the end of April, Node.js 10 goes out of LTS, which means I can target Node.js 12 in my packages. Node.js 12 has full ESM support! Required reading: https://nodejs.org/api/esm.html I plan to migrate most of my (1K+) packages to ESM within 2021. At the start of April, I will begin with some less popular packages, just to test the waters. I will use "type": "module" in package.json and not .mjs.
Record & Tuples から派生した JSON.parseImmutable というプロポーザルがよさそう
Records & Tuples というそこそこ有名(?)なプロポーザルがありますが、そのプロポーザルから派生した JSON.parseImmutable という新しいプロポーザルが良さそうなので紹介します。 Records & Tuples Records & Tuples はレコードとタプルという新しいデータ構造を導入する現在 Stage 2 のプロポーザルです。 レコードとタプルは、それぞれイミュータブルなオブジェクトと配列のようなものです。現在提案されている構文では通常のオブジェクトリテラルや配列リテラルの頭に # をつけると、レコードとタプルになります。 const record = #{ x: 1, y: 2, }; const tuple = #[1, 2, 3]; レコードやタプルやイミュータブルなデータ構造なので後から内容を更新することはできません。 レコードとタプルの大
ES2020 でリリースされた import.meta について - 30歳からのプログラミング
ES2020 でimport.metaがリリースされた。 この機能を使うと、モジュールのメタ情報を取得することができる。 例えば、当該モジュールのパスを取得することができる。 モジュールのメタ情報を取得する機能であるため、CommonJS や Script モードで使用するとエラーになる。 import.metaでどのような情報を取得できるか、Node.js、Deno、ブラウザで試してみた。 それぞれのバージョンは以下の通り。 Node.js: 14.7.0 Deno: 1.2.2 Google Chrome: 84.0.4147.105 Node.js 前述の通り CommonJS だとエラーになるため、ES Modules で使う必要がある。 // SyntaxError: Cannot use 'import.meta' outside a module console.log(im
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JavaScript Import maps, Part 1: Introduction
Release v4.0.0: ES2022 · asciidwango/js-primer
Re-implementing JavaScript's == in JavaScript
ECMAScript Annex B と型定義、ついでに ES2022 __proto__
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NodeJS Executable Standalone Module
遅延リストを扱うライブラリと ES2025 Iterator Helpers
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GitHub - lukeed/tsm: TypeScript Module Loader
ECMAScript仕様書を誰でも読めるようにする技術を求めて
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Ecma International approves ECMAScript 2024: What’s new?
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Ecma International approves ECMAScript 2022: What’s new?
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The triple dot syntax (`...`) in JavaScript: rest vs. spread
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ECMAScript仕様輪読会 #1 - esspec
What's new in ECMAScript 2023 | pawelgrzybek.com
The ESM move · sindresorhus/meta · Discussion #15