Debugging & Errors
How to Debug JavaScript in the Browser
Console logging that actually helps, breakpoints, stepping through code, and the Network tab — the four tools that solve nearly every front-end…
All guides
Every guide on the site, newest first. Explanations, projects and fixes written in plain English.
Debugging & Errors
Why Is My CSS Not Working? A Checklist
Your styles are not applying. Work through this ordered checklist — file linking, selector accuracy, specificity, inheritance and cascade order — to…
Debugging & Errors
How to Read a Stack Trace
A stack trace is a list of the function calls that led to an error. Here is how to read one in…
Debugging & Errors
Common JavaScript Errors and What They Mean
The JavaScript console errors beginners see most, what actually causes each one, and how to fix them — including the undefined error…
Debugging & Errors
Common Python Errors and How to Fix Them
The Python errors beginners hit most: SyntaxError, IndentationError, NameError, TypeError, ValueError, IndexError, KeyError and ModuleNotFoundError — each with a cause and a…
Debugging & Errors
How to Read Programming Errors (and Actually Fix Them)
Error messages are instructions, not insults. A repeatable method for reading any error, finding the real cause, and fixing it without guessing.
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…
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.