Dead Code Elimination

Oxc minifier supports eliminating dead code. For example, it removes the statements inside a if (false) block and the unused private class fields.

This feature is always enabled, but you can remove more code by enabling some options.

Useful features in the transformer

Other than the options below, you can also use the define feature in the transformer to replace global identifiers with constant expressions to remove more dead code.

Drop Console

You can remove all console.* calls by enabling the dropConsole option. This option behaves similar to Terser's drop_console option and esbuild's drop: ['console'] option.

// input
const bar = window.bar();
console.log("foo", bar, baz());

// output
const bar = window.bar();

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

const result = minify("lib.js", code, {
  compress: {
    dropConsole: true,
  },
});

The whole call expression is removed

Note that this option removes the whole call expression including the arguments. This is intentional because removing the evaluation of call arguments is useful for improving the runtime performance if those are expensive to compute. However, if any of those arguments have side effects, this transformation will change the behavior of your code.

Drop Debugger

You can remove all debugger statements by enabling the dropDebugger option. This option is enabled by default. This option behaves similar to Terser's drop_debugger option and esbuild's drop: ['debugger'] option.

// input
debugger;

// output

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

const result = minify("lib.js", code, {
  compress: {
    dropDebugger: true,
  },
});

Drop Labels

You can remove all labeled statements with specified labels by enabling the dropLabels option. This option behaves similar to esbuild's dropLabels option.

// input
DEV: console.log("foo");
console.log("bar");

// output
console.log("bar");

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

const result = minify("lib.js", code, {
  compress: {
    dropLabels: ["DEV"],
  },
});

Unused Declarations

All unused function / class / variable declarations are removed by default. You can keep them by using the unused option.

// input
{
  function foo() {}
}

// output

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

const result = minify("lib.js", code, {
  compress: {
    unused: true, // or "keep_assign"
  },
});

Keep name Property Values

By default, Oxc minifier assumes that your code does not rely on the name property of functions / classes. This is because the name property is inferred from the function / class name or the variable name and keeping the original name would prevent reducing the output size.

To keep the name property values, you can use the keepNames option.

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

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

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

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

mangle.keepNames option

If you are using the mangling feature, you may also want to enable the mangle.keepNames option.