Mangling

Oxc minifier can shorten variable names and selected property names.

Variable Names

Variable-name mangling is enabled by default. Set mangle to false to disable it, or pass an object to configure it. Use mangle.reserved to keep exact binding names unchanged and prevent Oxc from generating them.

Top-Level Variables

Top-level names are mangled by default in modules and CommonJS files, but not in scripts. Set mangle.toplevel to override this.

// input
var foo = 1;

// output
var e = 1;

// Example
import { minify } from "oxc-minify";

const result = await minify("lib.js", code, {
  mangle: {
    toplevel: true,
  },
});

Keep name Property Values

Mangling variable names can change the name property values of functions and classes. Set mangle.keepNames to preserve them.

// input
var foo = function () {};

// output
var foo = function () {};

// Example
import { minify } from "oxc-minify";

const result = await minify("lib.js", code, {
  mangle: {
    keepNames: true, // shorthand of { function: true, class: true }
  },
});

compress.keepNames option

When enabling this option, you may also want to enable the compress.keepNames option.

Debugging the Mangler

To debug the mangler, you can enable the mangle.debug option. When this option is enabled, the mangler will use slot_0, slot_1, ... as variable names.

// input
var foo = 1;

// output
var slot_0 = 1;

// Example
import { minify } from "oxc-minify";

const result = await minify("lib.js", code, {
  mangle: {
    debug: true,
    toplevel: true,
  },
});

Property Names

Property-name mangling is off by default. Use mangleProps.include to select the property names to mangle.

import { minify } from "oxc-minify";

const result = await minify("lib.js", code, {
  mangleProps: {
    include: /^_/,
    exclude: /^__public/,
    reserved: ["_externalApi"],
  },
});

exclude removes matching property names from the set selected by include. reserved keeps the listed exact names unchanged and also prevents Oxc from generating them as replacement names. Neither option adds entries to mangleCache by itself.

Quoted occurrences such as obj["_field"] are kept by default. This is handled per occurrence, so an unquoted use of the same name may still be mangled. Set quoted to true to mangle quoted occurrences too, or debug to true for readable generated property names.

The filters are JavaScript RegExp objects, but Oxc matches them with Rust's regex engine. It supports the i, m, s, and u flags and reports unsupported syntax or flags in result.errors.

To keep names stable when the source changes, reuse result.mangleCache as mangleProps.cache. A false cache entry keeps that property unchanged. Always start from unminified source; do not apply the same cache to already-mangled output.

WARNING

Only mangle properties owned by the code being minified. Oxc cannot safely update names built at runtime or used by unminified code. Exclude or reserve matching names used by public APIs, through module namespace objects, or on globals, DOM APIs, and other host APIs. A cache alone does not make separately minified files safe.

For more details, see the property-name assumptions.