About VisualizeJS

VisualizeJS is a free website that shows how JavaScript, React, Vue, Svelte, Angular, backend systems, and AI models work under the hood. Each topic is an animation you step through, with the code, the runtime state, and a written explanation side by side.

What is on the site

There are 45 topics across five areas: JavaScript (19), React (13), Frameworks (3), Backend (5), AI (5). They cover the mechanisms people get asked about in interviews and run into in real bugs, such as the event loop, closures, React reconciliation, the HTTP request lifecycle, database indexes, and attention in transformer models.

Every topic page has the same layout. The source code sits next to panels that show what the engine is doing, for example the call stack, the component tree, a request moving between services, or a matrix of attention weights. Below the animation there is a theory section with the mechanism, common mistakes, and interview questions.

How the content is made

Each visualization is written by hand. The steps, the line of code highlighted on each step, and the values in each panel are authored in the open source repository, and an automated check confirms that every step points at the right line before a release.

If you find something that is wrong or unclear, please report it. Accuracy matters more here than any new feature.

Who makes it

VisualizeJS is built and maintained by Tornike Nizharadze. The site is free, needs no account, and shows no ads. The code is open source under the MIT license.