Beautify and format JavaScript code instantly — indent minified JS, add line breaks and produce readable code with proper indentation and spacing.
Enter your figures and click Calculate to see your results.
Paste your JavaScript code, choose to beautify or analyze, then select your indent preference.
Click the Format button. Your code is processed instantly — all formatting runs in your browser with no data sent to servers.
The formatted output appears on the right. Click Copy to grab it, or Download to save as a file. Statistics like size reduction and line count are shown automatically.
Consistent code formatting reduces cognitive load when reading others' code, makes code reviews faster (reviewers focus on logic, not style), prevents trivial whitespace changes from cluttering version control diffs, and catches obvious style inconsistencies early. Tools like ESLint (linting) and Prettier (formatting) are standard in professional JavaScript development to enforce consistent style automatically.
Formatting (what this tool does) controls whitespace, indentation, line breaks and bracket placement — purely cosmetic changes that do not affect code behaviour. Linting (e.g. ESLint) checks for code quality issues: unused variables, undeclared variables, potential bugs, accessibility problems and style violations. Formatters and linters are complementary — most teams run both in their CI/CD pipeline.
Prettier is the most popular opinionated JavaScript formatter. It takes code as input and reprints it according to its own style rules, ignoring your original formatting. It supports JS, TypeScript, JSX, CSS, SCSS, HTML, JSON, GraphQL, Markdown and more. Unlike configurable formatters, Prettier has very few options (intentionally) to eliminate style debates in teams. This online tool provides quick formatting without needing to install Prettier locally.
Semicolons are technically optional in JavaScript due to Automatic Semicolon Insertion (ASI). However, ASI has edge cases that cause bugs — particularly when a line starts with (, [, /, +, or -. Most style guides (Google, Airbnb) recommend using semicolons. Some (StandardJS) recommend omitting them. Prettier can format either way consistently. The important thing is choosing one style and applying it consistently throughout a project.
== performs abstract equality comparison with type coercion: "5" == 5 is true, null == undefined is true, 0 == false is true. === performs strict equality with no type coercion: "5" === 5 is false, null === undefined is false. Always use === unless you specifically need type coercion (rare). Most linters flag == as a warning (prefer-strict-equality rule) because type coercion produces counterintuitive results.
CommonJS (CJS) uses require() and module.exports — the original Node.js module system. ES Modules (ESM) uses import and export — the standard in modern JavaScript, supported natively in browsers and Node.js 14+. ESM enables static analysis and tree-shaking (removing unused code). Most new projects use ESM. Bundlers (webpack, Rollup, Vite) handle interoperability between the two systems.
Tree-shaking is a dead code elimination technique used by JavaScript bundlers. It analyses import/export statements statically to identify which exported functions are actually used, then removes the rest from the bundle. For example, if you import { format } from 'date-fns', only the format function is included — not the entire date-fns library. Tree-shaking only works with ESM (not CommonJS) because ESM imports are static and analysable at build time.
JavaScript is single-threaded — it can only execute one piece of code at a time. The event loop is the mechanism that allows asynchronous behaviour without multithreading: synchronous code runs on the call stack; async operations (setTimeout, fetch, I/O) are offloaded to Web APIs; when complete, their callbacks are queued in the task queue (macrotasks) or microtask queue (Promises); the event loop processes these when the call stack is empty.
