js-codemod

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

Setup & Run

npm install -g jscodeshift
git clone https://github.com/cpojer/js-codemod.git
jscodeshift -t <codemod-script> <file>

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

Included Scripts

arrow-function

Transforms functions to arrow functions

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

It will transform function() { }.bind(this) calls to () => {}. If the only statement in the body is a ReturnStatement it will remove the curly braces. 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 --inline-single-expressions=true option and it will transform function() { relay(); }.bind(this) to () => relay() instead of () => { relay(); }.

use-strict

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

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

object-shorthand

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

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

template-literals

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.

unquote-properties

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

jscodeshift -t js-codemod/transforms/unquote-properties.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"}'