Writing JavaScript tools in other languages – a new trend?
Writing JavaScript tools in other languages – a new trend? Recently, we have seen an uptick of JavaScript tools being written in languages other than JavaScript. This blog post lists a few examples and explains the appeal of not using JavaScript. Examples # I asked on Twitter and these are a few of the examples that people mentioned: Build tools and compilers: esbuild – Go: JavaScript bundler and
Alternatives to enums in TypeScript
A recent blog post explored how TypeScript enums work. In this blog post, we take a look at alternatives to enums. Unions of singleton values # An alternative to creating an enum that maps keys to values, is to create a union of singleton types (one per value). Read on to see how that works. Unions of string literal types # Let’s start with an enum and convert it to a union of string literal typ
A class-based enum pattern for JavaScript
In this blog post, we examine a pattern for implementing enums in JavaScript that is based on classes. We’ll also take a look at Enumify, a library that helps with the enum pattern. Implementing enums: first attempts # An enum is a type that consists of a set of values. For example, TypeScript has built-in enums and with them, we can define our own boolean type: enum MyBoolean { false, true, } Or
ECMAScript 2020: the final feature set
Update 2020-04-02: Today, the ES2020 candidate was released, with the final feature set of that version. This blog post describes what’s new. A word on ECMAScript versions # Note that since the TC39 process was instituted, the importance of ECMAScript versions has much decreased. What really matters now is what stage a proposed feature is in: Once it has reached stage 4, it can be used safely. Bu
Hybrid npm packages (ESM and CommonJS)
Warning: This blog post is outdated. It may contain incorrect information. Update 2019-11-22: ESM support in Node.js is not experimental, anymore. This post was updated to reflect that. Conditional exports are now explained. In this blog post, we look at npm packages that contain both ES modules and CommonJS modules. Required knowledge: How ES modules are supported natively on Node.js. You can rea
Evaluating JavaScript code via `import()`
The import() operator lets us dynamically load ECMAScript modules. But they can also be used to evaluate JavaScript code (as Andrea Giammarchi recently pointed out to me), as an alternative to eval(). This blog post explains how that works. eval() does not support export and import # A significant limitation of eval() is that it doesn’t support module syntax such as export and import. If we use i
Unpacking hoisting
The following sections describe the behavior of some of these constructs in more detail. const and let: temporal dead zone # For JavaScript, TC39 needed to decide what happens if you access a constant in its direct scope, before its declaration: { console.log(x); // What happens here? const x; } Some possible approaches are: The name is resolved in the scope surrounding the current scope. You get
ES2018: RegExp lookbehind assertions
The proposal “RegExp Lookbehind Assertions” by Gorkem Yakin, Nozomu Katō, Daniel Ehrenberg is part of ES2018. This blog post explains it. A lookaround assertion is a construct inside a regular expression that specifies what the surroundings of the current location must look like, but has no other effect. It is also called a zero-width assertion. The only lookaround assertion currently supported by
ES2018: RegExp named capture groups
The proposal “RegExp Named Capture Groups” by Gorkem Yakin, Daniel Ehrenberg is at stage 4. This blog post explains what it has to offer. Before we get to named capture groups, let’s take a look at numbered capture groups; to introduce the idea of capture groups. Numbered capture groups # Numbered capture groups enable you to take apart a string with a regular expression. Successfully matching a
The new ECMAScript module support in Node.js 12
Follow-up blog post: “Hybrid npm packages (ESM and CommonJS)” Node.js 12 (which was released on 2019-04-23) brings improved support for ECMAScript modules. It implements phase 2 of the plan that was released late last year. For now, this support is available behind the usual flag --experimental-modules. Read on to find out how exactly this new support for ECMAScript modules works. Brief spoiler: T
Feature watch: ECMAScript 2019
Update 2019-01-29: The feature set of ECMAScript 2019 is now final (source) and described in this blog post. A word on ECMAScript versions # Note that since the TC39 process was instituted, the importance of ECMAScript versions has much decreased. What really matters now is what stage a proposed feature is in: Once it has reached stage 4, it can be used safely. But even then, you still have to ch
Future JavaScript: what is still missing?
In recent years, JavaScript has grown considerably in size. This blog post explores what’s still missing. Notes: I’m only listing the missing features that I find most important. Many others are useful, but there is also a risk of adding too much. My choices are subjective. Almost everything mentioned in this blog post is on TC39’s radar. That is, it also serves as a preview of a possible future J
ECMAScript modules in Node.js: the new plan
Status of ECMAScript module (ESM) support in Node.js: Experimental support for ESM was added in Node.js 8.5.0 (2017-09-12). Afterwards, the Node.js Foundation Technical Steering Committee formed the Modules Team to help design missing pieces and to guide the implementation towards its (non-experimental) release. The Modules Team is comprised of people from several different web development areas (
JavaScript vs. TypeScript vs. ReasonML
In this blog post, I describe the pros and cons of three programming languages/dialects: JavaScript, TypeScript and ReasonML. My descriptions are based on recent experiences with TypeScript and ReasonML on a few smaller real-world projects and on years of experience with JavaScript. Before we take a look at the languages, let’s first consider the pros and cons of static typing, given that TypeScri
What is ReasonML?
[2018-02-08] Warning: outdated content. Read the book “Exploring ReasonML”, instead (free online). This blog post gives a brief high-level explanation of Facebook’s new programming language, ReasonML. Blog posts in this series # Background: What is ReasonML [this blog post] Getting started with ReasonML What is planned for ReasonML? Core language: Basic values and types let bindings and scopes Pa
Currying is not idiomatic in JavaScript
Update 2017-11-18a: I worded a few things more carefully, to make it clear that I don’t hate functional programming (I’m a fan). Update 2017-11-18b: I added subsections to Sect. “Currying is in conflict with some of JavaScript’s foundations”. In this blog post I explain why, in my opinion, currying is in conflict with some of JavaScript’s foundations. Recommended reading if you are not sure what c
ES proposal: `import.meta` – module metadata
The proposal “import.meta” by Domenic Denicola is currently at stage 3. This blog post explains how it works. Module metadata # When it comes to working with a module, you are normally interested in what’s inside it. But occasionally, you need information about the module – its metadata. One example of module metadata for Node.js modules is the global variable __dirname which contains the path of
Using ES modules natively in Node.js
Update 2018-12-20: Warning: This blog post is outdated! Consult “ECMAScript modules in Node.js: the new plan” for the latest information. Update 2017-09-14: Major rewrite of Sect. “Checklist: things to watch out for”. New FAQ entries. Starting with version 8.5.0, Node.js supports ES modules natively, behind a command line option. Most of the credit for this new functionality goes to Bradley Farias
ECMAScript 6’s new array methods
Check out my book (free online): “Exploring ES6”. Updated version of this blog post: chapter “New Array features”. This blog post explains what new array methods ECMAScript 6 will bring and how to use them in current browsers. Note: I’m using the terms constructor and class interchangeably. Class methods # Array has gained methods of its own. Array.from(arrayLike, mapFunc?, thisArg?) # Array.fro
Configuring Babel 6
Update: This series of blog post has been turned into the book “Setting up ES6” (which is free to read online). Babel 6 is much more configurable than Babel 5, but also more difficult to configure. This blog post gives tips. Follow-up blog posts: [2015-12-11] Babel 6: configuring ES6 standard library and helpers [2015-12-12] Babel 6: loose mode [2015-12-13] Babel and CommonJS modules Installing Ba
リリース、障害情報などのサービスのお知らせ
最新の人気エントリーの配信
j次のブックマーク
k前のブックマーク
lあとで読む
eコメント一覧を開く
oページを開く
