JavaScript Minifier

Compress JavaScript with Terser — dead-code elimination, name mangling and expression folding.

MinifiersRuns in your browserFree, no sign-up

Options

Compress

Dead-code elimination, constant folding, expression simplification.

Mangle names

Shortens local variable names. Never renames globals or properties.

Input is an ES module

Enables module-scope assumptions. Wrong for classic <script> code.

Keep comments

Preserve /*! ... */ banner comments such as licence headers.

JavaScript input

Minified JavaScript

Output appears here as you type.

Ctrl + Enter to run

About the JavaScript Minifier

This runs Terser, which renames local variables, removes unreachable branches and collapses expressions. Stripping whitespace alone typically saves 20 to 30 percent; Terser on the same file usually saves 60 or more, and the difference is entirely the transformations whitespace removal cannot safely attempt.

Those savings survive compression, unlike whitespace, and they reduce parse time in the browser as well as bytes on the wire. Test the output if your code relies on function or constructor names, since renaming breaks reflection-based libraries in ways that only appear at runtime.

Frequently asked questions

Why does the "ES module" switch matter?

It tells Terser it may assume module semantics — strict mode, and that top-level declarations are not global. That unlocks better compression, but it is wrong for a classic <script>, where a top-level var genuinely does become a global that other scripts may read. Enabling it for non-module code can produce a broken bundle.

Is name mangling safe?

For local variables, yes — Terser only renames bindings whose entire scope it can see. Globals and object properties are left alone by default, because it cannot know whether something outside the file reads them. Code that uses eval() or with() defeats the analysis and should not be mangled.

How much smaller will my code get?

Typically 30–60% before gzip for unminified source, and more for code with long identifiers and many comments. The savings figure above the output reports the exact number for your input.