ES6 Lenses changelog

Proxy-powered functional lenses for ECMAScript 2015+ & TypeScript projects (try it in your browser now!)

// Install: `npm i --save es6-lenses`
const {lens, _} = require("es6-lenses")
const obj = {x: {y: 1}, z: 2}

// Flow / TypeScript alternative:
//   lens((_: typeof obj) => _.x.y)
const xy = lens(_.x.y)
// Lenses can be called (== .get):
xy(obj) // 1
xy.get(obj) // 1
// Set deep-clones the modified paths:
xy.set(obj, 10) // {x: {y: 10}, z: 2}

// Shorthand selectors are also functions:
[{x: 1}, {x: 2}].map(_.x) // [1, 2]

// Lenses can create nested structures:
const y_z = lens([_.x.y, {z: _.z}])
y_z.get(obj) // ['y', {z: 'z'}]
y_z.set(obj, ['yy', {z: 'zz'}])
// {x: {y: 'yy'}, z: 'zz'}

Note: .set deeply clones objects (and is Immutable.Map-aware), while .mutate attempts to modify them in-place.

About lenses

• Functional Lenses, How Do They Work
• Lenses with Immutable.js
• Great pre-existing lens libraries (see npmjs):
  • https://github.com/DrBoolean/lenses
  • https://github.com/calmm-js/partial.lenses
  • https://github.com/roman01la/js-lenses
  • https://github.com/fantasyland/fantasy-lenses
  • https://github.com/tomasdeml/lenticular.ts
  • https://github.com/beezee/statelens

About Proxies

• Metaprogramming in ES6:

  • http://www.2ality.com/2014/12/es6-proxies.html
  • https://ponyfoo.com/articles/es6-proxy-traps-in-depth
  • https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Meta_programming

• Proxy docs:

  • https://github.com/tvcutsem/harmony-reflect/blob/master/doc/traps.md
  • https://github.com/Microsoft/TypeScript/blob/master/lib/lib.es2015.proxy.d.ts

TODO

• Support filtered / mapped semantics: lens(_ => _.addresses.map(_ => _.zipCode)).mapped.update(toUpperCase)
• More examples about tuple / object inputs & outputs.
• More tests, especially re/ integration with Immutable (cover interaction w/ Record)

Bundling with rollup

Notes:

• Can't down-compile to ES5 as we're using ES6's Proxy
• UglifyJS might require a special ES6-friendly branch: please report any success :-)

Setup:

• Prerequisite:

  npm --save-dev rollup
  npm --save-dev rollup-watch
  npm --save-dev rollup-plugin-typescript
  npm --save-dev rollup-plugin-node-resolve

• Config (rollup.config.js):

  import typescript from 'rollup-plugin-typescript';
  import nodeResolve from 'rollup-plugin-node-resolve';
  
  export default {
    entry: './main.ts',
    format: 'iife',
    dest: 'out.js',
    sourceMap: true,
    plugins: [
      nodeResolve({jsnext: true, main: true}),
      typescript({
        typescript: require('typescript')
      }),
    ]
  }

• Add the following scripts to your package.json:

  {
    "scripts": {
      "rollup": "rollup -c",
      "rollup:w": "rollup -c -w"
    },
    ...
  }

• Build with npm run rollup, continuously rebuild with npm run rollup:w

Develop

npm i
npm start