Tutorial

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

When to use Map and Set instead of objects and arrays, and what the weak versions are for.

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

Pattern syntax, flags, testing and replacing, named groups, and when a regex is the wrong tool.

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

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.

Read error messages, log effectively, set breakpoints and step through code in browser DevTools.

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

Global, function and block scope, hoisting of declarations, and why let and const throw before declaration.

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

How functions remember their surrounding scope, practical uses, and common closure bugs.

Class syntax, constructors, methods, private fields, static members and extends.