Minification

Starting with v1.2.67, you can configure SWC to minify your code by enabling minify in your .swcrc file:

{
  // Enable minification
  "minify": true,
  // Optional, configure minifcation options
  "jsc": {
    "minify": {
      "compress": {
        "unused": true
      },
      "mangle": true
    }
  }
}

Configuration#

Note about comments#

If you set jsc.minify.compress to true or {}, SWC will remove all comments. If you don't want this, modify jsc.minify.format.

jsc.minify.compress#

Type: boolean | object.

Similar to the compress option of terser.

{
  "jsc": {
    "minify": {
      "compress": true // equivalent to {}
    }
  }
}

• arguments, defaults to false.
• arrows, defaults to true.
• booleans, defaults to true.
• booleans_as_integers, defaults to false.
• collapse_vars, defaults to true.
• comparisons, defaults to true.
• computed_props, defaults to true.
• conditionals, defaults to true.
• dead_code, defaults to false.
• defaults, defaults to true.
• directives, defaults to true.
• drop_console, defaults to false.
• drop_debugger, defaults to true.
• ecma, defaults to 5.
• evaluate, defaults to true.
• global_defs, defaults to {}.
• hoist_funs, defaults to false.
• hoist_props, defaults to true.
• hoist_vars, defaults to false.
• ie8, Ignored.
• if_return, defaults to true.
• inline, defaults to true.
• join_vars, defaults to true.
• keep_classnames, defaults to false.
• keep_fargs, defaults to false.
• keep_infinity, defaults to false.
• loops, defaults to true.
• negate_iife, defaults to true.
• passes, defaults to 0, which means no limit.
• properties, defaults to true.
• pure_getters, defaults to ``.
• pure_funcs, defaults to []. Type is an array of string.
• reduce_funcs, defaults to false.
• reduce_vars, defaults to true.
• sequences, defaults to true.
• side_effects, defaults to true.
• switches, defaults to true.
• top_retain, defaults to ``.
• toplevel, defaults to true.
• typeofs, defaults to true.
• unsafe, defaults to false.
• unsafe_arrows, defaults to false.
• unsafe_comps, defaults to false.
• unsafe_Function, defaults to false.
• unsafe_math, defaults to false.
• unsafe_symbols, defaults to false.
• unsafe_methods, defaults to false.
• unsafe_proto, defaults to false.
• unsafe_regexp, defaults to false.
• unsafe_undefined, defaults to false.
• unused, defaults to true.
• module, Ignored. Currently, all files are treated as module.

jsc.minify.mangle#

Type: boolean | object.

Similar to the mangle option of terser.

{
  "jsc": {
    "minify": {
      "mangle": true // equivalent to {}
    }
  }
}

• properties, Defaults to false, and true is identical to {}.
• topLevel, Defaults to true. Aliased as toplevel for compatibility with terser.
• keepClassNames, Defaults to false. Aliased as keep_classnames for compatibility with terser.
• keepFnNames, Defaults to false.
• keepPrivateProps, Defaults to false. Aliased as keep_private_props for compatibility with terser.
• reserved, Defaults to []
• ie8, Ignored.
• safari10, Not implemented yet.

jsc.minify.mangle.properties#

Type: object.

Similar to the mangle properties option of terser.

{
  "jsc": {
    "minify": {
      "mangle":{
        "properties":{
          "reserved": ["foo", "bar"],
          "undeclared":false,
          "regex":"rust regex"
        }
      }
    }
  }
}

• reserved: Don't use these names as properties.

• undeclared: Mangle properties even if it's not delcared.

• regex: Mangle properties only if it matches this regex

jsc.minify.format#

These properties are mostly not implemented yet, but it exists to support passing terser config to swc minify without modification.

• asciiOnly, Defaults to false. Implemented as v1.2.184 and aliased as ascii_only for compatibility with terser.
• beautify, Defaults to false. Currently noop.
• braces, Defaults to false. Currently noop.
• comments, Defaults to false.
  • false removes all comments
  • 'some' preserves some comments
  • 'all' preserves all comments
• ecma, Defaults to 5. Currently noop.
• indentLevel, Currently noop and aliases as indent_level for compatibility with terser.
• indentStart, Currently noop and aliases as indent_start for compatibility with terser.
• inlineScript, Currently noop and aliases as inline_script for compatibility with terser.
• keepNumbers, Currently noop and aliases as keep_numbers for compatibility with terser.
• keepQuotedProps, Currently noop and aliases as keep_quoted_props for compatibility with terser.
• maxLineLen, Currently noop, and aliases as max_line_len for compatibility with terser.
• preamble, Currently noop
• quoteKeys, Currently noop and aliases as quote_keys for compatibility with terser.
• quoteStyle, Currently noop and aliases as quote_style for compatibility with terser.
• preserveAnnotations, Currently noop and aliases as preserve_annotations for compatibility with terser.
• safari10, Currently noop.
• semicolons, Currently noop.
• shebang, Currently noop.
• webkit, Currently noop.
• wrapIife, Currently noop and aliases as wrap_iife for compatibility with terser.
• wrapFuncArgs, Currently noop and aliases as wrap_func_args for compatibility with terser.

@swc/core Usage#

swc.minify(code, options)#

This API is asynchronous and all of parsing, minification, and code generation will be done in background thread. The options argument is same as jsc.minify object. For example:

import swc from "@swc/core";

const { code, map } = await swc.minify(
  "import foo from '@src/app'; console.log(foo)",
  {
    compress: false,
    mangle: true,
  }
);

expect(code).toMatchInlineSnapshot(`"import a from'@src/app';console.log(a);"`);

Returns Promise<{ code: string, map: string }>.

swc.minifySync(code, options)#

This API exists on @swc/core, @swc/wasm, @swc/wasm-web.

import swc from "@swc/core";

const { code, map } = swc.minifySync(
  "import foo from '@src/app'; console.log(foo)",
  {
    compress: false,
    mangle: true,
  }
);

expect(code).toMatchInlineSnapshot(`"import a from'@src/app';console.log(a);"`);

Returns { code: string, map: string }.

APIs for WebAssembly#

Replacing Terser#

You can reduce build time and override Terser without needing a library to update their dependencies through yarn resolutions. Example package.json would include:

{
  "resolutions": { "terser": "npm:@swc/core" }
}

This will use the SWC minifier instead of Terser for all nested dependencies. Ensure you remove your lockfile and re-install your dependencies.

$ rm -rf node_modules yarn.lock
$ yarn