JavaScript Formatter and Minifier

How to format or minify JavaScript

1. Paste your code, or click Open a file to load a .js, .mjs or .jsx file (up to 10 MB).
2. Choose the Indentation and, if you prefer the Allman style, tick Braces on their own line.
3. Click Format (beautify) to make the code readable.
4. To shrink it, set the Minify options and click Minify. To only look for errors, click Check syntax.
5. Copy or download the result. The status line shows the size before and after, and the percentage saved.

The code is only read and transformed, never run: nothing you paste is executed on this page.

Beautify with js-beautify

Format (beautify) uses js-beautify. It puts one statement per line, indents blocks, adds spaces around operators and after keywords, and keeps up to one blank line where you had some. It also understands modern syntax (classes, arrow functions, template literals, async/await) and JSX. It is the quickest way to read a minified library or a one-line snippet copied from a web page.

Beautifying only changes whitespace. It does not check that the code is valid: a missing parenthesis simply produces odd indentation. Use Check syntax for that.

Minify with Terser

Minify uses Terser, the minifier used by most JavaScript build tools. Because it is large, it is only downloaded when you first click Minify or Check syntax. The options map directly to Terser settings:

• ES module (import/export) parses the code as a module (module: true): strict mode applies and top-level names are private, so they can be renamed and unused ones removed. Leave it unticked for a classic script whose global functions are used by other scripts.
• Compress (compress) rewrites the code into shorter equivalent code: constant folding (2*60 becomes 120), dead code removal, joining of var declarations, shorter conditions.
• Shorten variable names (mangle) renames local variables and parameters to one or two letters. Global names and object properties are never renamed.
• Keep license comments keeps comments that start with /*! or contain @license or @preserve. All other comments are removed.

Minification cannot change what the code does, but code that relies on function names (fn.name) or on eval can behave differently after renaming. Untick Shorten variable names in that case.

Syntax errors with line and column

When Terser cannot parse the code, Minify and Check syntax show the error message with its line and column, for example “Line 12, column 8 – Syntax error: Unexpected token punc «)»”. The column counts characters from 1. A typical cause is a missing bracket earlier in the file, so look at the lines just before the reported position too.