Format JavaScript and JSX with parser-aware quotes, semicolons and trailing commas, explicit syntax errors and local worker processing before review.
Specialist tool for FormattingLive, copy-ready output1 guided projectPrivate in your browser
Use this result well
A quick decision brief for this specific tool
Inputs that matter
JavaScript input
Output to expect
Formatted JavaScript
How it works
A dedicated interactive panel for this data format or operation
Start with the included valid sample, then replace it with your own input.
Review errors and compare the output before replacing source data.
Choose your path
Built around the job you need to finish
Produce a reviewable JavaScript or JSX formatting diff that respects comments, regex literals, templates and automatic semicolon insertion.
Frontend author
Format JS/JSX without damaging URLs, comments, regexes or templates.
Paste the authored example, choose quote/indent preferences, format and compare source/output.
Receives parser-generated code and copy-only output without appended reports.
Code reviewer
Understand semicolon and trailing-comma semantics.
Compare both semicolon styles around for loops and return-newline cases, challenge syntax errors, then recover.
No invalid partial output; formatting is not confused with linting, type checking or execution.
Keyboard project user
Review and hand off settings without stale output.
Use labeled keyboard controls, change options, rerun and explicitly save to the Project.
Only current output is copyable/savable; JavaScript warning does not collide with SQL.
Authoritative checks for this tool
Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.
Prettier 3.9.6 uses Babel and ESTree plugins. Comments, regex literals and template syntax are parsed before printing. Embedded-language formatting is disabled; source code is never evaluated.
Bounded local execution
An explicit run loads the language engine in a disposable worker. Cancellation and a wall-clock timeout prevent abandoned work from updating results. Input code is never executed.
Review current output
Input or option changes invalidate old output. Copy/download contain code only, not an appended report. Formatting is not automatic repair or runtime validation.
Updated: August 2026
Example Scenarios
Format URL strings, regex literals and nested templates without regex-based substitutions that corrupt their contents.
Correct an incomplete function using the displayed parser error, then format again to replace the empty result.
Save source, formatted JavaScript and a distinct settings/warning note to the REST API Project after checking ASI-sensitive code.
FAQ
The formatter handles syntax rather than removing every semicolon. It retains grammar-required separators and may insert leading semicolons to avoid automatic-semicolon-insertion hazards.
This route supports JavaScript and JSX through Babel, not TypeScript. Formatting does not type-check, lint, execute, transpile or secure code.
No. Quote preference may yield to fewer escapes; JSX quotes have their own behavior. Print width is a target, not a maximum. Trailing commas in function calls require ES2017-compatible runtimes.
Code is processed in a local worker, not uploaded or automatically saved. Engine assets may need a connection on first use. An explicit Project save stores source, result and notes on this device; do not save secrets.
Input is limited to 100,000 characters and output to 300,000. Runs stop after 10 seconds. File imports are limited to 400,000 bytes; Project saves require source and output each within 100,000 characters. Editing input or settings requires a new run.
About JavaScript Formatter
Use the Babel parser through Prettier for JavaScript and JSX. Choose indentation, width target, quote preference, semicolons and trailing commas; compare the result before replacing source.