Package Exports

gen-codemod

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (gen-codemod) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

gen-codemod

Generate codemods by comparing your initial JavaScript to your desired JavaScript.

Usage

gen-codemod INITIAL.js DESIRED.js > my-transform.js

INITIAL.js is a JavaScript file containing the initial, pre-codemod JavaScript that you'd like to change.

DESIRED.js is a JavaScript file containing the desired, post-codemod JavaScript that you'd like to have.

gen-codemod compares these two files and creates a codemod to get from INITIAL.js to DESIRED.js.

Example

When upgrading from sinon.js v1 -> v2, every instance of sinon.stub(obj, method, fn) is changed to sinon.stub(obj, method).andCallsFake(fn). We can generate this codemod as follows:

echo "sinon.stub(A, B, C)" > sinon-v1.js
echo "sinon.stub(A, B).andCallFake(C)" > sinon-v2.js
gen-codemod sinon-v1.js sinon-v2.js

Note: Single uppercase letters, such as A, B, C, etc, are used as variables and match anything.

This outputs:

module.exports = function(file, api) {
  const j = api.jscodeshift;

  const rootProperties = {
    type: 'CallExpression',
    callee: {
      type: 'MemberExpression',
      object: { type: 'Identifier', name: 'sinon' },
      property: { type: 'Identifier', name: 'stub' },
      computed: false
    },
    arguments: [{}, {}, {}]
  };

  function getTransform(path) {
    return j.callExpression(
      j.memberExpression(
        j.callExpression(
          j.memberExpression(
            j.identifier('sinon'),
            j.identifier('stub'),
            false
          ),
          [getANode(path), getBNode(path)]
        ),
        j.identifier('andCallsFake'),
        false
      ),
      [getCNode(path)]
    );
  }

  function getANode(path) {
    return path.node.arguments[0];
  }
  function getBNode(path) {
    return path.node.arguments[1];
  }
  function getCNode(path) {
    return path.node.arguments[2];
  }

  return j(file.source)
    .find(j.CallExpression, rootProperties)
    .replaceWith(getTransform)
    .toSource();
};

To run your codemod, use jscodeshift:

gen-codemod sinon-v1.js sinon-v2.js > my-transform.js
npx jscodeshift -t my-transform.js PATH_TO_TRANSFORM

Install

npm i -g gen-codemod

Limitations

Can't change multiple AST expressions at once (only reads the first AST node from the initial / desired JavaScript files).