codemod

codemod rewrites JavaScript and TypeScript using babel plugins.

Install

Install from npm:

$ npm install @codemod/cli

This will install the runner locally as codemod. This package requires node v16 or higher. This README assumes you've installed locally, but you can also install globally with npm install -g @codemod/cli.

Usage

The primary interface is as a command line tool, usually run like so:

$ npx codemod --plugin transform-module-name \
  path/to/file.js \
  another/file.js \
  a/directory

This will re-write the files path/to/file.js, another/file.js, and any supported files found in a/directory by transforming them with the babel plugin transform-module-name. Multiple plugins may be specified, and multiple files or directories may be re-written at once.

Note that TypeScript support is provided by babel and therefore may not completely support all valid TypeScript code. If you encounter an issue, consider looking for it in the babel issues labeled area: typescript before filing an issue.

Plugins may also be loaded from remote URLs, including saved AST Explorer URLs, using --remote-plugin. This feature should only be used as a convenience to load code that you or someone you trust wrote. It will run with your full user privileges, so please exercise caution!

$ npx codemod --remote-plugin URL …

By default, codemod makes minimal changes to your source files by using recast to parse and print your code, retaining the original comments and formatting. If desired, you can reformat files using Prettier or ESLint or whatever other tools you prefer after the fact.

For more detailed options, run npx codemod --help.

Writing a Plugin

There are many, many existing plugins that you can use. However, if you need to write your own you should consult the babel handbook. If you publish a plugin intended specifically as a codemod, consider using both the babel-plugin and babel-codemod keywords.

@codemod/cli provides a few helpers to make writing codemod plugins easier. For example:

/**
 * This codemod rewrites `A * A` to `A ** 2` for any expression `A`.
 */
import { defineCodemod } from '@codemod/cli'

// `m` is `@codemod/matchers`, a library of useful matchers
// `t` is `@babel/types`, babel AST type predicates and builders
export default defineCodemod(({ t, m }) => {
  // `operand` is a capture matcher that will be filled in by `multiplyBySelf`,
  // which is a binary expression matcher that matches any expression multiplied
  // by itself.
  const operand = m.capture(m.anyExpression())
  const multiplyBySelf = m.binaryExpression(
    '*',
    operand,
    m.fromCapture(operand)
  )

  return {
    visitor: {
      BinaryExpression(path) {
        m.match(multiplyBySelf, { operand }, path.node, ({ operand }) => {
          path.replaceWith(
            t.binaryExpression('**', operand, t.numericLiteral(2))
          )
        })
      },
    },
  }
})

Transpiling using Babel Plugins

codemod supports parsing language features supported by a standard Babel or TypeScript build toolchain, similar to what a Create React App build pipeline can handle. Feel free to write your plugins using these language features–they'll be transpiled on the fly.

Passing Options to Plugins

You can pass a JSON object as options to a plugin:

# Pass a JSON object literal
$ npx codemod --plugin ./my-plugin.ts --plugin-options '{"opt": true}'
# Pass a JSON object from a file
$ npx codemod --plugin ./my-plugin.ts --plugin-options @opts.json

Contributing

See CONTRIBUTING.md for information on setting up the project for development and on contributing to the project.

License

Copyright 2017 Brian Donovan

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.