JavaScript Code Playground — Run & Debug JS Online

About the JavaScript Playground

Code Visualizer’s JavaScript playground lets you write, execute, and visualize JavaScript code in real-time. Paste any JS snippet — from simple loops to complex async/await chains — and watch as the event loop spins, the call stack grows and shrinks, closures capture variables, and promises move through the microtask queue.

Set breakpoints on any line, step through function calls one at a time, and inspect the full program state at every point. Whether you’re debugging a tricky callback order, learning how closures work, preparing for a frontend interview, or teaching a CS course, this interactive JavaScript debugger makes complex execution flows intuitive.