ECMAScript 2024 features: resizing and transferring ArrayBuffers
ECMAScript 2024 features: resizing and transferring ArrayBuffers In this blog post, we examine ArrayBuffer features that were introduced in ECMAScript 2024: “In-place resizable ArrayBuffers”, proposed by Shu-yu Guo “ArrayBuffer.prototype.transfer and friends” proposed by Shu-yu Guo, Jordan Harband and Yagiz Nizipli What are ArrayBuffers? # The following classes provide an API for handling binary
ECMAScript 2023 feature: symbols as WeakMap keys
In this blog post, we take a look at the ECMAScript 2023 feature “Symbols as WeakMap keys” – which was proposed by Robin Ricard, Rick Button, Daniel Ehrenberg, Leo Balter, Caridy Patiño, Rick Waldron, and Ashley Claymore. What are WeakMaps good for? # The key ability of a WeakMap is to associate data with a value: The value is the key of a WeakMap entry. The data is the value of that entry. Consi
ECMAScript 2024 feature: `Promise.withResolvers()`
In this blog post we take a look at the ECMAScript 2024 feature “Promise.withResolvers” (proposed by Peter Klecha). It provides a new way of directly creating Promises, as an alternative to new Promise(...). new Promise(...) – the revealing constructor pattern # Before Promise.withResolvers(), there was only one way to create Promises directly – via the following pattern: const promise = new Prom
JavaScript metaprogramming with the 2022-03 decorators API
More information on the syntax and semantics of decorators (optional section) # (This section is optional. If you skip it, you can still understand the remaining content.) The syntax of decorator expressions # A decorator expression starts with a chain of one or more identifiers, separated by dots. Each identifier except the first one can be private (prefix #). Square brackets [] are not allowed
ECMAScript proposal: iterator helpers
Update 2022-12-15: New section “How will this proposal affect future JavaScript APIs?” In this blog post, we look at the ECMAScript proposal “Iterator helpers” by Gus Caplan, Michael Ficarra, Adam Vandolder, Jason Orendorff, Kevin Gibbons, and Yulia Startsev. It introduces utility methods for working with iterable data: .map(), .filter(), .take(), etc. The style of the proposed API clashes with th
ECMAScript proposal: RegExp flag `/v` makes character classes and character class escapes more powerful
ECMAScript proposal: RegExp flag /v makes character classes and character class escapes more powerful In this blog post, we look at the ECMAScript proposal “RegExp v flag with set notation + properties of strings” by Markus Scherer and Mathias Bynens. The new flag /v # The proposed new regular expression flag /v (.unicodeSets) enables three features: Support for multi-code-point graphemes (such a
TypeScript and native ESM on Node.js
In this blog post, I’ll explain everything you need to know in order to use and produce native ECMAScript modules on Node.js. The GitHub repository iterable is an example of a TypeScript ESM package that works on Node.js. It still uses the "typesVersions" workaround (which isn’t needed in TypeScript 4.7 and later). (Thanks to Guy Beford and Oleg Drapeza for their feedback on this post.) TypeScript
Temporal: getting started with JavaScript’s new date time API
Temporal: getting started with JavaScript’s new date time API Updates: 2022-01-10: Temporal.now was renamed to Temporal.Now. 2021-06-30: Rearranged the content and created a section on the concepts and patterns used by the Temporal API. 2021-06-29: Clarified how Instant uses the ISO-8601 calendar. Listed the properties of some classes. Date, JavaScript’s current date time API is infamously difficu
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
Three useful Babel presets
As of version 6, Babel supports presets, sets of features that can be enabled together. This blog post looks at three new useful Babel presets (and, as a bonus, two presets especially for Node.js). Complementing or replacing babel-preset-es2015 # These two presets are useful complements to babel-preset-es2015 (for ES6): babel-preset-es2016 gives you one of the two features of ES2016: the exponent
DOM: element IDs are global variables
Several tweets mentioned that in order to display an element in Chrome’s JavaScript console, you only have to type its ID. @johnjbarton pointed out that that is because all element IDs are global variables. This blog post explains a few more details. The standard The HTML5 standard specifies that the window object must have a property key whose value is elem if... there is exactly one DOM element
Safe integers in JavaScript
Update 2014-02-08: Follow-up blog post “What are integers in JavaScript?” JavaScript can only safely represent integers i in the range −253 < i < 253. This blog post examines why that is and what “safely represent” means. It is based on an email by Mark S. Miller to the es-discuss mailing list. The idea of a safe integer is about how mathematical integers are represented in JavaScript. In the rang
asm.js: closing the gap between JavaScript and native
Update 2013-12-30: New feature 32 bit floats pushes asm.js performance to 70% of native. More JavaScript engines support asm.js. The conclusion mentions LLJS as another asm.js source language. asm.js defines a subset of JavaScript that can be compiled to fast executables. It has been created at Mozilla by David Herman, Luke Wagner and Alon Zakai. According to the specification, “[asm.js] effective
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