Nifty Pony Merchandise


    0.7.1 • Public • Published

    jscodeshift Build Status

    jscodeshift is a toolkit for running codemods over multiple JavaScript or TypeScript files. It provides:

    • A runner, which executes the provided transform for each file passed to it. It also outputs a summary of how many files have (not) been transformed.
    • A wrapper around recast, providing a different API. Recast is an AST-to-AST transform tool and also tries to preserve the style of original code as much as possible.


    Get jscodeshift from npm:

    $ npm install -g jscodeshift

    This will install the runner as jscodeshift.

    Usage (CLI)

    The CLI provides the following options:

    $ jscodeshift --help
    Usage: jscodeshift [OPTION]... PATH...
      or:  jscodeshift [OPTION]... -t TRANSFORM_PATH PATH...
      or:  jscodeshift [OPTION]... -t URL PATH...
      or:  jscodeshift [OPTION]... --stdin < file_list.txt
    Apply transform logic in TRANSFORM_PATH (recursively) to every PATH.
    If --stdin is set, each line of the standard input is used as a path.
    "..." behind an option means that it can be supplied multiple times.
    All options are also passed to the transformer, which means you can supply custom options that are not listed here.
          --(no-)babel              apply babeljs to the transform file
                                    (default: true)
      -c, --cpus=N                  start at most N child processes to process source files
                                    (default: max(all - 1, 1))
      -d, --(no-)dry                dry run (no changes are made to files)
                                    (default: false)
          --extensions=EXT          transform files with these file extensions (comma separated list)
                                    (default: js)
      -h, --help                    print this help and exit
          --ignore-config=FILE ...  ignore files if they match patterns sourced from a configuration file (e.g. a .gitignore)
          --ignore-pattern=GLOB ...  ignore files that match a provided glob expression
          --parser=babel|babylon|flow|ts|tsx  the parser to use for parsing the source files
                                              (default: babel)
          --parser-config=FILE      path to a JSON file containing a custom parser configuration for flow or babylon
      -p, --(no-)print              print transformed files to stdout, useful for development
                                    (default: false)
          --(no-)run-in-band        run serially in the current process
                                    (default: false)
      -s, --(no-)silent             do not write to stdout or stderr
                                    (default: false)
          --(no-)stdin              read file/directory list from stdin
                                    (default: false)
      -t, --transform=FILE          path to the transform file. Can be either a local path or url
                                    (default: ./transform.js)
      -v, --verbose=0|1|2           show more information about the transform process
                                    (default: 0)
          --version                 print version and exit

    This passes the source of all passed through the transform module specified with -t or --transform (defaults to transform.js in the current directory). The next section explains the structure of the transform module.

    Transform module

    The transform is simply a module that exports a function of the form:

    module.exports = function(fileInfo, api, options) {
      // transform `fileInfo.source` here
      // ...
      // return changed source
      return source;

    As of v0.6.1, this module can also be written in TypeScript.



    Holds information about the currently processed file.

    Property Description
    path File path
    source File content


    This object exposes the jscodeshift library and helper functions from the runner.

    Property Description
    jscodeshift A reference to the jscodeshift library
    stats A function to collect statistics during --dry runs
    report Prints the passed string to stdout

    jscodeshift is a reference to the wrapper around recast and provides a jQuery-like API to navigate and transform the AST. Here is a quick example, a more detailed description can be found below.

     * This replaces every occurrence of variable "foo".
    module.exports = function(fileInfo, api) {
      return api.jscodeshift(fileInfo.source)

    Note: This API is exposed for convenience, but you don't have to use it. You can use any tool to modify the source.

    stats is a function that only works when the --dry options is set. It accepts a string, and will simply count how often it was called with that value.

    At the end, the CLI will report those values. This can be useful while developing the transform, e.g. to find out how often a certain construct appears in the source(s).

    report allows you do print arbitrary strings to stdout. This can be useful when other tools consume the output of jscodeshift. The reason to not directly use process.stdout in transform code is to avoid mangled output when many files are processed.


    Contains all options that have been passed to runner. This allows you to pass additional options to the transform. For example, if the CLI is called with

    $ jscodeshift -t myTransforms fileA fileB --foo=bar

    options would contain {foo: 'bar'}.

    Return value

    The return value of the function determines the status of the transformation:

    • If a string is returned and it is different from passed source, the transform is considered to be successful.
    • If a string is returned but it's the same as the source, the transform is considered to be unsuccessful.
    • If nothing is returned, the file is not supposed to be transformed (which is ok).

    The CLI provides a summary of the transformation at the end. You can get more detailed information by setting the -v option to 1 or 2.

    You can collect even more stats via the stats function as explained above.


    The transform can let jscodeshift know with which parser to parse the source files (and features like templates).

    To do that, the transform module can export parser, which can either be one of the strings "babel", "babylon", "flow", "ts", or "tsx", or it can be a parser object that is compatible with recast.

    For example:

    module.exports.parser = 'flow'; // use the flow parser
    // or
    module.exports.parser = {
      parse: function(source) {
        // return estree compatible AST

    Example output

    $ jscodeshift -t myTransform.js src
    Processing 10 files...
    Spawning 2 workers with 5 files each...
    All workers done.
    Results: 0 errors 2 unmodified 3 skipped 5 ok

    The jscodeshift API

    As already mentioned, jscodeshift also provides a wrapper around recast. In order to properly use the jscodeshift API, one has to understand the basic building blocks of recast (and ASTs) as well.

    Core Concepts

    AST nodes

    An AST node is a plain JavaScript object with a specific set of fields, in accordance with the Mozilla Parser API. The primary way to identify nodes is via their type.

    For example, string literals are represented via Literal nodes, which have the structure

    // "foo"
      type: 'Literal',
      value: 'foo',
      raw: '"foo"'

    It's OK to not know the structure of every AST node type. The (esprima) AST explorer is an online tool to inspect the AST for a given piece of JS code.

    Path objects

    Recast itself relies heavily on ast-types which defines methods to traverse the AST, access node fields and build new nodes. ast-types wraps every AST node into a path object. Paths contain meta-information and helper methods to process AST nodes.

    For example, the child-parent relationship between two nodes is not explicitly defined. Given a plain AST node, it is not possible to traverse the tree up. Given a path object however, the parent can be traversed to via path.parent.

    For more information about the path object API, please have a look at ast-types.


    To make creating AST nodes a bit simpler and "safer", ast-types defines a couple of builder methods, which are also exposed on jscodeshift.

    For example, the following creates an AST equivalent to foo(bar):

    // inside a module transform
    var j = jscodeshift;
    // foo(bar);
    var ast = j.callExpression(

    The signature of each builder function is best learned by having a look at the definition files.

    Collections and Traversal

    In order to transform the AST, you have to traverse it and find the nodes that need to be changed. jscodeshift is built around the idea of collections of paths and thus provides a different way of processing an AST than recast or ast-types.

    A collection has methods to process the nodes inside a collection, often resulting in a new collection. This results in a fluent interface, which can make the transform more readable.

    Collections are "typed" which means that the type of a collection is the "lowest" type all AST nodes in the collection have in common. That means you cannot call a method for a FunctionExpression collection on an Identifier collection.

    Here is an example of how one would find/traverse all Identifier nodes with jscodeshift and with recast:

    // recast
    var ast = recast.parse(src);
    recast.visit(ast, {
      visitIdentifier: function(path) {
        // do something with path
        return false;
    // jscodeshift
      .forEach(function(path) {
        // do something with path

    To learn about the provided methods, have a look at the Collection.js and its extensions.


    jscodeshift provides an API to extend collections. By moving common operators into helper functions (which can be stored separately in other modules), a transform can be made more readable.

    There are two types of extensions: generic extensions and type-specific extensions. Generic extensions are applicable to all collections. As such, they typically don't access specific node data, but rather traverse the AST from the nodes in the collection. Type-specific extensions work only on specific node types and are not callable on differently typed collections.


    // Adding a method to all Identifiers
    	logNames: function() {
    		return this.forEach(function(path) {
    }, jscodeshift.Identifier);
    // Adding a method to all collections
    	findIdentifiers: function() {
    		return this.find(jscodeshift.Identifier);
    jscodeshift(ast).logNames(); // error, unless `ast` only consists of Identifier nodes

    Passing options to recast

    You may want to change some of the output settings (like setting ' instead of "). This can be done by passing config options to recast.

    .toSource({quote: 'single'}); // sets strings to use single quotes in transformed code.

    You can also pass options to recast's parse method by passing an object to jscodeshift as second argument:

    jscodeshift(source, {...})

    More on config options here

    Unit Testing

    jscodeshift comes with a simple utility to allow easy unit testing with Jest, without having to write a lot of boilerplate code. This utility makes some assumptions in order to reduce the amount of configuration required:

    • The test is located in a subdirectory under the directory the transform itself is located in (eg. __tests__)
    • Test fixtures are located in a __testfixtures__ directory

    This results in a directory structure like this:


    A simple example of unit tests is bundled in the sample directory.

    The testUtils module exposes a number of useful helpers for unit testing.


    Defines a Jest/Jasmine test for a jscodeshift transform which depends on fixtures

    const defineTest = require('jscodeshift/dist/testUtils').defineTest;
    defineTest(__dirname, 'MyTransform');

    An alternate fixture filename can be provided as the fourth argument to defineTest. This also means that multiple test fixtures can be provided:

    defineTest(__dirname, 'MyTransform', null, 'FirstFixture');
    defineTest(__dirname, 'MyTransform', null, 'SecondFixture');

    This will run two tests:

    • __testfixtures__/FirstFixture.input.js
    • __testfixtures__/SecondFixture.input.js


    Defines a Jest/Jasmine test suite for a jscodeshift transform which accepts inline values

    This is a more flexible alternative to defineTest, as this allows to also provide options to your transform

    const defineInlineTest = require('jscodeshift/dist/testUtils').defineInlineTest;
    const transform = require('../myTransform');
    const transformOptions = {};
    defineInlineTest(transform, transformOptions, 'input', 'expected output', 'test name (optional)');


    Similar to defineInlineTest but instead of requiring an output value, it uses Jest's toMatchSnapshot()

    const defineSnapshotTest = require('jscodeshift/dist/testUtils').defineSnapshotTest;
    const transform = require('../myTransform');
    const transformOptions = {};
    defineSnapshotTest(transform, transformOptions, 'input', 'test name (optional)');

    For more information on snapshots, check out Jest's docs


    Executes your transform using the options and the input given and returns the result. This function is used internally by the other helpers, but it can prove useful in other cases.

    const applyTransform = require('jscodeshift/dist/testUtils').applyTransform;
    const transform = require('../myTransform');
    const transformOptions = {};
    const output = applyTransform(transform, transformOptions, 'input');

    Example Codemods

    • react-codemod - React codemod scripts to update React APIs.
    • js-codemod - Codemod scripts to transform code to next generation JS.
    • js-transforms - Some documented codemod experiments to help you learn.



    npm i @robmarr/jscodeshift

    DownloadsWeekly Downloads






    Unpacked Size

    1.41 MB

    Total Files


    Last publish


    • robinmarr