fn-to-class-codemod

This is a codemod script for use with jscodeshift. It will transform ES5 constructor-function-based "classes" into ES6 classes.

There are existing tools for this that didn't cover my specific case, which involves specific use of lodash's extend function. For the common case, where e.g. methods are defined with Foo.prototype.bar = ..., you should instead use one of these:

• lebab
• dhruvdutt/es5-function-to-class-codemod

Example

fn-to-class-codemod will transform code like this:

import { extend } from 'lodash'
import Entity from './entity'

export default function Hint (game, tile) {
  Entity.call(this, game, tile)
  this.isFlat = true
}

extend(Hint.prototype, Entity.prototype)

extend(Hint.prototype, {
  collideWith: function (target) {
    this.moveHere(target)
    this.game.hintPanel.show()
  }
})

...to this:

import { extend } from 'lodash'
import Entity from './entity'

export default class Hint extends Entity {
  constructor(game, tile, emap) {
    super(game, tile, emap)
    this.isFlat = true
  }

  collideWith(target) {
    this.moveHere(target)
    this.game.hintPanel.show()
  }
}

Note that the unused import has not been removed (but a followup eslint --fix pass should do it though.

Using

To use this codemod to modify files in place:

npm install --global jscodeshift
jscodeshift -t fn-to-class.js $your_file_or_dir

I recommend that you first do a console-printed dry run with:

jscodeshift -d -p -t fn-to-class.js ...

To do

• preserve comments in all cases
• transform properties
• test with multiple classes per file

Things that this doesn't handle, which I don't necessarily plan on adding

• support the common case (prototype.bar = )
• support _.extend, _.assignIn, and assignIn
• support Object.extend
• partially-transformed files (later steps rely on the class declaration having been created in the same session)

Developing

Pull requests are very welcome. Note that ESLint is declared as a dev dependency at the moment -- this is just for my own convenience.

hub clone johncip/fn-to-class-codemod
cd fn-to-class-codemod
npm install