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sdgluck · Mar 26, 2017 · a066030 · a066030
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diff --git a/.gitignore b/.gitignore
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+node_modules
+.idea
diff --git a/README.md b/README.md
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+# mewt
+
+> :ant: Immutability in under a kilobyte
+
+## Install
+
+```sh
+npm install --save mewt
+```
+
+```sh
+yarn add mewt
+```
+
+## Import
+
+```js
+// ES2015
+import immutable from 'mewt'
+```
+
+```js
+// CommonJS
+var immutable = require('mewt')
+```
+
+## Usage
+
+```js
+const arr = immutable([])
+
+// all array instance methods are available
+const [,arr1] = arr.push('bubble')
+console.log(arr1 === arr) //=> false
+
+// methods with return value also return new array
+const [val, arr2] = arr1.pop()
+console.log(val) //=> 'bubble'
+console.log(arr2 === arr1) //=> false
+```
+
+## API
+
+Create an immutable instance from a JavaScript array or object:
+
+```js
+let immutableArray = immutable([])
+let immutableObect = immutable({})
+```
+
+### Array
+
+### Object
diff --git a/index.js b/index.js
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+/** Create immutable instance of array or object.
+ *  @returns {Array|Object} */
+module.exports = function mewt (target) {
+  let current = target
+    , isArr = Array.isArray(target)
+    , multiRet = ['push', 'pop', 'shift', 'unshift']
+    , clone = v => isArr ? [].concat(v) : Object.assign({}, v)
+
+  let override = fn => (...args) => {
+    let res = current[fn](...args)
+    current = clone(current)
+    return multiRet.includes(fn) ? [res, current] : current
+  }
+
+  if (!isArr && typeof target !== 'object')
+    throw new Error('mewt accepts array or object')
+
+  return new Proxy(target, {
+    set: (_, prop, val) => (current = clone(current), current[prop] = val, true),
+    get: (_, prop) => current[prop] && (current.hasOwnProperty(prop) ? current[prop] : override(prop))
+  })
+}
diff --git a/package.json b/package.json
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+{
+  "name": "mewt",
+  "version": "1.0.0",
+  "description": "Immutability in under a kilobyte",
+  "main": "index.js",
+  "scripts": {
+    "test": "node test"
+  },
+  "author": "Sam Gluck <sdgluck@gmail.com>",
+  "license": "MIT",
+  "devDependencies": {
+    "tape": "^4.6.3"
+  }
+}
diff --git a/test.js b/test.js
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+'use strict'
+
+const test = require('tape')
+const mewt = require('./index')
+
+test('exports a function', (t) => {
+  t.equal(typeof mewt, 'function')
+  t.end()
+})
+
+test('throws without object or array', (t) => {
+  t.throws(() => mewt(), /accepts array or object/)
+  t.end()
+})
+
+test('array', (t) => {
+  {
+    // returns new array
+    const a = []
+    const n = mewt([])
+    t.notEqual(a, n)
+  }
+  {
+    // copyWithin
+    const a = mewt([1, 2])
+    const n = a.copyWithin(0, 2)
+    t.deepEqual(n, [1, 2])
+    t.notEqual(a, n)
+  }
+  {
+    // fill
+    const a = mewt([,])
+    const n = a.fill('')
+    t.deepEqual(n, [''])
+    t.notEqual(a, n)
+  }
+  {
+    // pop
+    const a = mewt([''])
+    const [str, n] = a.pop()
+    t.equal(str, '')
+    t.deepEqual(n, [])
+    t.notEqual(a, n)
+  }
+  {
+    // push
+    const a = mewt([])
+    const [len, n] = a.push('')
+    t.equal(1, len)
+    t.deepEqual(n, [''])
+    t.notEqual(a, n)
+  }
+  {
+    // reverse
+    const a = mewt([1, 2])
+    const n = a.reverse()
+    t.deepEqual(n, [2, 1])
+    t.notEqual(a, n)
+  }
+  t.end()
+})