Tutorials

A reference of ECMAScript features from ES2015 onwards, what each solves, and how to check support.

Separate logic from the DOM, pure functions, dependency injection and small modules that are easy to test.

What V8 and other engines do with your code, optimisation and deoptimisation, and what that means for everyday code.

Unique property keys with Symbol, and customising language behaviour with Symbol.iterator and friends.

Cancel work with AbortController, add timeouts, retry with exponential backoff and avoid race conditions.

API design, defaults and options objects, error messages, types, versioning and publishing to npm.

Transform and search arrays with built-in methods, chaining, and which methods mutate.

Unpack arrays and objects, copy and merge with spread, and collect arguments with rest.

Object.keys, values and entries, shallow versus deep copies with structuredClone, and Object.freeze.

Read nested data safely with ?. and supply defaults with ?? without treating 0 and empty strings as missing.

Convert between objects and JSON text, handle parse errors, and what JSON cannot represent.

The Date object and its pitfalls, formatting dates, numbers and currencies with Intl, and the Temporal API.

Build elements with createElement, insert them with append and before, use template elements, and remove nodes.

How events travel through the DOM, stopping propagation, and handling many elements with one listener.

Why JavaScript is asynchronous, callback functions, and the problems that led to promises.

Create and consume promises, chaining with then, error handling with catch, and finally.

Write asynchronous code that reads top to bottom, handle errors with try and catch, and run tasks in parallel.

Request JSON from an API with fetch, check response status, and show loading and error states.

Split code into modules with named and default exports, use modules in the browser, and dynamic import.

Throw and catch errors, error types, custom error classes, and handling async errors.