JavaScript Formatter

Most of the time you reach for a JavaScript formatter, the goal is comprehension rather than style. A file arrives as a single line — from a bundle, a CDN, a CMS field, a minified vendor script — and the question is what it does. Restoring the line structure is what makes that answerable: control flow becomes visible, function boundaries become obvious, and you can set a breakpoint on something meaningful. It does not recover names or comments, but it turns an unreadable wall of text into code you can reason about.

For your own codebase, formatting should be automatic and invisible. Configure Prettier once, enable format-on-save, and run it in a pre-commit hook so that style stops being something anyone discusses in review. The payoff is not prettier code so much as cleaner diffs: when formatting is deterministic, every changed line in a pull request is a real change. Manual formatting is what you do for foreign code, which is exactly the case this tool covers.

No. Formatting only adjusts whitespace and line breaks, which JavaScript ignores between tokens, so the program behaves identically. The one place where newlines can matter is automatic semicolon insertion, and a formatter is careful not to introduce a break that would change how statements terminate. If your code relies on omitted semicolons in unusual places, format it and run your tests — but for ordinary code this is a safe, purely cosmetic transformation.

It can make minified code readable, but it cannot undo minification. Formatting restores the indentation and line structure, so you can follow the control flow — but names that a minifier shortened to a, b, and n are gone for good, because the original identifiers were discarded when the file was built. If a sourcemap was published alongside the bundle, that is the only way to get the real source back, and browser devtools will use it automatically.

For code you own, use Prettier in your editor and on commit — it enforces one style across a whole codebase without anybody thinking about it, and it understands JSX, TypeScript, and your project config. This tool is for code that is not in your project: a snippet from a Stack Overflow answer, a minified file you are trying to understand, output from a build you want to inspect, or something pasted into a chat that arrived as one long line.

Plain TypeScript and JSX generally format acceptably, because the underlying structure is the same as JavaScript. Type annotations, generics, and JSX attributes are treated as ordinary tokens rather than understood as syntax, so complex generic signatures or deeply nested JSX may not break lines the way a TypeScript-aware formatter would. For real TypeScript work, Prettier with a TypeScript parser is the right tool; this is for quick inspection.

No. Everything runs in your browser as JavaScript — your code is never uploaded, never logged, and never sent to a server. You can verify that by watching the Network tab in devtools while you work, or by disconnecting from the internet after the page loads and confirming the tools still function. Nothing you paste is executed either; it is only ever parsed as text.