JavaScript
JavaScript localStorage Explained
How to save data in the browser so it survives a refresh: setItem and getItem, storing objects with JSON, and the corrupted-value…
JavaScript
How JavaScript actually works in the browser. Variables, functions, the DOM, events and async code, explained with examples you can paste into a console.
11 guides
JavaScript
JavaScript Array Methods: A Reference
Every array method worth knowing, grouped by what you are trying to do, with a one-line example each and a clear table…
JavaScript
JavaScript Fetch API: Getting Data From the Internet
How to request data with fetch, read a JSON response, send data with POST, handle errors properly, and show a loading state.
JavaScript
JavaScript Async and Await Explained
Why some code finishes later, what a promise is, and how async/await lets you write waiting code that still reads top to…
JavaScript
JavaScript Events Explained
How to react to clicks, typing and form submissions. Event listeners, the event object, preventDefault, and delegation for elements that do not…
JavaScript
JavaScript DOM Basics: Changing a Web Page
How to select elements, change text and styles, add and remove elements, and why your script sometimes cannot find anything on the…
JavaScript
JavaScript Objects Explained
How objects store labelled data, dot versus bracket access, destructuring, spreading, and how to avoid the "cannot read properties of undefined" error.
JavaScript
JavaScript Arrays Explained (Including map, filter and reduce)
Creating arrays, adding and removing items, and the three methods you will use constantly — map, filter and reduce — explained with…
JavaScript
JavaScript Functions and Arrow Syntax Explained
Function declarations, expressions and arrow functions — what the differences are, when each is right, and how callbacks fit in.
JavaScript
JavaScript Variables: let, const and var Explained
Which keyword to use and why. Scope, hoisting, reassignment versus mutation, and why const objects can still be changed.
JavaScript
JavaScript for Beginners: How It Actually Works
What JavaScript is, where it runs, and the core syntax you need. Includes a first script you can run in your browser…
Related topics
Where to go next
Programming Basics
The ideas every language shares — variables, loops, functions and how a program actually runs.
10 guides
Python
Plain-English Python guides, from your first line of code to small programs that do real work.
14 guides
Web Development
HTML, CSS and the pieces that turn code into a page people can visit.
4 guides
Keep going — pick your next guide
The fastest way to improve is to read one guide, then build the thing it describes. Start with the basics, or jump straight to a project.