Ecma International approves ECMAScript 2025: What’s new? 🔗
<p>On 25 June 2025, the 129th Ecma General Assembly approved the ECMAScript 2025 language specification (<a href="https://ecma-international.org/news/ [...]
2ality – JavaScript and more
Posts
Tips for making regular expressions easier to use in JavaScript 🔗
<p>In this blog post, we explore ways in which we can make regular expressions easier to use.</p> [...]
TypeScript: checking Map keys and Array indices 🔗
<p>JavaScript has two common patterns:</p> <ul> <li>Maps: We check the existence of a key via <code>.has()</code> before retrieving the associated val [...]
How TypeScript solved its global <code>Iterator</code> name clash 🔗
<p>In ECMAScript 2025, JavaScript gets a class <code>Iterator</code> with iterator helper methods. This class conflicts with TypeScript’s existing typ [...]
Styling console text in Node.js 🔗
<p>In this blog post, we explore how we can style text that we log to the console in Node.js.</p> <p>Some of the examples use a Unix shell but most of [...]
Converting values to strings in JavaScript has pitfalls 🔗
<p>Converting values to strings in JavaScript is more complicated than it might seem:</p> <ul> <li>Most approaches have values they can’t handle.</li> [...]
Deploying TypeScript: recent advances and possible future directions 🔗
<p>In this blog post we look at:</p> <ul> <li>The current best practice for deploying library packages: <code>.js</code>, <code>.js.map</code>, <code> [...]
Ideas for making TypeScript better at testing types 🔗
<p>In this blog post, we examine how we can test types in TypeScript:</p> <ul> <li>First, we look at the library <code>asserttt</code> and the CLI too [...]
Could JavaScript have synchronous <code>await</code>? 🔗
<p>In JavaScript, code has <em>color</em>: It is either synchronous or asynchronous. In this blog post, we explore:</p> <ul> <li>The problems caused b [...]
A closer look at the details behind the Go port of the TypeScript compiler 🔗
<p>Today’s <a href="https://devblogs.microsoft.com/typescript/typescript-native-port/">announcement</a> by Microsoft:</p> <blockquote> <p>[...] we’ve [...]
Unions and intersections of object types in TypeScript 🔗
<p>In this blog post, we explore what unions and intersections of object types can be used for in TypeScript.</p> [...]
My sales pitch for TypeScript 🔗
<p>Roughly, TypeScript is JavaScript plus type information. The latter is removed before TypeScript code is executed by JavaScript engines. Therefore, [...]
What is TypeScript? An overview for JavaScript programmers 🔗
<p>Read this blog post if you are a JavaScript programmer and want to get a rough idea of what using TypeScript is like (think first step before learn [...]
Simple TypeScript playgrounds via <code>node --watch</code> 🔗
<p>Now that Node.js has <a href="https://2ality.com/2025/01/nodejs-strip-type.html">built-in support for TypeScript</a>, we can use it as the foundati [...]
Testing types in TypeScript 🔗
<p>In this blog post, we explore how we can test that complicated TypeScript types work as expected. To do that, we need assertions at the type level [...]
The unexpected way in which conditional types constrain type variables in TypeScript 🔗
<p>The TypeScript handbook makes an interesting <a href="https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#conditional-type-constr [...]
The bottom type <code>never</code> in TypeScript 🔗
<p>In this blog post, we look at the special TypeScript type <code>never</code> which, roughly, is the type of things that never happen. As we’ll see, [...]
Array type notations: <code>T[]</code> vs. <code>Array<T></code> in TypeScript 🔗
<p>In this blog post, we explore two equivalent notations for Arrays in TypeScript: <code>T[]</code> and <code>Array<T></code>. I prefer the lat [...]
Symbols in TypeScript 🔗
<p>In this blog post, we examine how TypeScript handles JavaScript symbols at the type level.</p> <p>If you want to refresh your knowledge of JavaScri [...]
Conditional types in TypeScript 🔗
<p>A conditional type in TypeScript is an if-then-else expression: Its result is either one of two branches – which one depends on a condition. That i [...]
Mapped types in TypeScript 🔗
<p>A mapped type is a loop over keys that produces an object or tuple type and looks as follows:</p> <pre><code class="language-ts">{[<span class="hlj [...]
TypeScript: extracting parts of compound types via <code>infer</code> 🔗
<p>In this blog post, we explore how we can extract parts of compound types via the <code>infer</code> keyword.</p> <p>It helps if you are loosely fam [...]
TypeDoc: testing code examples in doc comments 🔗
<p>TypeDoc now lets us refer to parts of other files via <code>{@includeCode}</code>. In this blog post, I explain how that works and why it’s useful. [...]
TypeScript: the <code>satisfies</code> operator 🔗
<p>TypeScript’s <code>satisfies</code> operator lets us check the type of a value (mostly) without influencing it. In this blog post, we examine how e [...]
Read-only accessibility in TypeScript 🔗
<p>In this blog post, we look at how can make things “read-only” in TypeScript – mainly via the keyword <code>readonly</code>.</p> [...]
Tutorial: publishing ESM-based npm packages with TypeScript 🔗
<p>During the last two years, ESM support in TypeScript, Node.js and browsers has made a lot of progress. In this blog post, I explain my modern setup [...]
Computing with tuple types in TypeScript 🔗
<p>JavaScript’s Arrays are so flexible that TypeScript provides two different kinds of types for handling them:</p> <ul> <li>Array types for arbitrary [...]
Template literal types in TypeScript: parsing during type checking and more 🔗
<p>In this blog post, we take a closer look at template literal types in TypeScript: While their syntax is similar to JavaScript’s template literals, [...]
ECMAScript 2025 feature: RegExp escaping 🔗
<p>The ECMAScript proposal <a href="https://github.com/tc39/proposal-regex-escaping">“RegExp escaping”</a> (by Jordan Harband and Kevin Gibbons) speci [...]
TypeScript enums: use cases and alternatives 🔗
<p>In this blog post, we take a closer look at TypeScript enums:</p> <ul> <li>How do they work?</li> <li>What are their use cases?</li> <li>What are t [...]
A guide to <code>tsconfig.json</code> 🔗
<p>I never felt confident about my <code>tsconfig.json</code>. To change that, I went through the <a href="https://www.typescriptlang.org/tsconfig/">o [...]
ECMAScript 2025 feature: regular expression pattern modifiers 🔗
<p>Traditionally, we could only apply regular expression flags such as <code>i</code> (for ignoring case) to all of a regular expression. The ECMAScri [...]
ECMAScript feature: import attributes 🔗
<p>The ECMAScript feature <a href="https://github.com/tc39/proposal-import-attributes">“Import Attributes”</a> (by Sven Sauleau, Daniel Ehrenberg, Myl [...]
Node’s new built-in support for TypeScript 🔗
<p>Starting with <a href="https://nodejs.org/en/blog/release/v23.6.0">v23.6.0</a>, Node.js supports TypeScript without any flags. This blog post expla [...]
WebAssembly as an ecosystem for programming languages 🔗
<p>In this blog post, we look at how WebAssembly has become an ecosystem for many programming languages and what technologies enable that.</p> [...]