Leporello.js – interactive functional programming IDE for JavaScript

In plain words

Leporello.js is an interactive development environment for functional JavaScript that executes code instantly as you type and displays results alongside it. It includes a debugger accessible by positioning the cursor on any line to see values immediately, and visualizes the program's call tree. Users can navigate forward and backward through execution, similar to time-travel debugging. The tool supports interactive HTML5 application development while preserving application state, and records and replays IO traces during subsequent executions.

written from the facts on this page · September 2026

From the sources

Online JavaScript/TypeScript playground and debugger

Click a DOM element to jump to its corresponding JSX in the debugger. Inspect all related variables, arguments, and expressions in context. Read more Support us on GitHub Sponsors and be the first to gain access to the Leporello.js Visual Studio Code plugin with TypeScriptfrom leporello.tech

In the maker’s words, at launch

Hi! Leporello.js is an interactive functional programming environment designed for pure functional subset of JavaScript. It executes code instantly as you type and displays results next to it. Leporello.js also features an omnipresent debugger. Just position your cursor on any line or select any expression, and…

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