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Bump y18n from 3.2.1 to 3.2.2 (#110)
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js-codemod Build Status

This repository contains a collection of codemod scripts for use with JSCodeshift.

Setup & Run

npm install -g jscodeshift
git clone
jscodeshift -t <codemod-script> <file>

Use the -d option for a dry-run and use -p to print the output for comparison.

Included Scripts


jscodeshift -t js-codemod/transforms/arrow-function-arguments.js <file>


Transforms callbacks only when it can guarantee it won't break this context in the function. Also transforms function() { }.bind(this) calls to () => {}.

jscodeshift -t js-codemod/transforms/arrow-function.js <file>

--inline-single-expressions=true: If you are feeling lucky and you know that returning the value of single-expression functions will not affect the behavior of your application you can specify the option and it will transform function() { relay(); } to () => relay() instead of () => { relay(); }.

--max-width=120: Try the best it can to keep line lengths under the specified length.


jscodeshift -t js-codemod/transforms/invalid-requires.js <file>


jscodeshift -t js-codemod/transforms/jest-update.js <file>


Converts functions to not reassign to parameters. This is useful to turn on in conjunction with Flow's const_params option.

jscodeshift -t js-codemod/transforms/no-reassign-params.js <file>


Conservatively converts var to const or let.

jscodeshift -t js-codemod/transforms/no-vars.js <file>


Transforms object literals to use ES6 shorthand for properties and methods.

jscodeshift -t js-codemod/transforms/object-shorthand.js <file>


jscodeshift -t js-codemod/transforms/outline-require.js <file>


jscodeshift -t js-codemod/transforms/rm-copyProperties.js <file>


jscodeshift -t js-codemod/transforms/rm-merge.js <file>


jscodeshift -t js-codemod/transforms/rm-object-assign.js <file>


Removes any requires where the imported value is not referenced. Additionally if any module is required more than once the two requires will be merged.

jscodeshift -t js-codemod/transforms/rm-requires.js <file>


Replaces string concatenation with template literals.

jscodeshift -t js-codemod/transforms/template-literals.js <file>

Adapted from "How to write a codemod" by Ramana Venkata.

Areas of improvement:

  • Comments in the middle of string concatenation are currently added before the string but after the assignment. Perhaps in these situations, the string concatenation should be preserved as-is.

  • Nested concatenation inside template literals is not currently simplified. Currently, a + b${'c' + d} becomes ${a}b${'c' + d} but it would ideally become ${a}b${`c${d}`}.

  • Unnecessary escaping of quotes from the resulting template literals is currently not removed. This is possibly the domain of a different transform.

  • Unicode escape sequences are converted to unicode characters when the simplified concatenation results in a string literal instead of a template literal. It would be nice to perserve the original--whether it be a unicode escape sequence or a unicode character.


jscodeshift -t js-codemod/transforms/touchable.js <file>


Adds trailing commas to array and object literals.

jscodeshift -t js-codemod/transforms/trailing-commas.js <file>


Unchains chained variable declarations.

jscodeshift -t js-codemod/transforms/unchain-variables.js <file>


Replaces underscore (or lodash) to ES6 + lodash, preferring native ES6 array methods. Member imports are used by default to allow tree-shaking, but the --split-imports=true option will split each lodash import into its own lodash/<method> import.

jscodeshift -t js-codemod/transforms/underscore-to-lodash-native.js <file>


Removes quotes from object properties whose keys are strings which are valid identifiers.

jscodeshift -t js-codemod/transforms/unquote-properties.js <file>


jscodeshift -t js-codemod/transforms/updated-computed-props.js <file>


Adds a top-level 'use strict' statement to JavaScript files

jscodeshift -t js-codemod/transforms/use-strict.js <file>

Included extensions

jscodeshift-imports helpers for modifying import and require statements, see docs.

Recast Options

Options to recast's printer can be provided through the printOptions command line argument

jscodeshift -t transform.js <file> --printOptions='{"quote":"double"}'