JavaScript code visualizer
Free JavaScript code visualizer: run JavaScript step by step and see the call stack, objects, closures, promises and the event loop, with each line explained.
Opening the visualizer…
About the JavaScript code visualizer
StepVioz runs your JavaScript in the browser's own engine, in strict mode, and records every step: each function's variables, and objects, arrays, Maps, Sets and class instances drawn in the heap with arrows between them. Conditions are worked out with their values.
After the main script, the event loop is shown as it really runs: promise callbacks first, then each timer in time order, with async functions leaving and rejoining the call stack. console.log prints as Node.js does, and prompt() reads lines from the input box.