Have you ever thought about immutable version of Array.prototype methods?
For example, Array.prototype.push return a new Array instead of number of items.

I've created immutable-array-prototype package.

Why immutable?

ECMAScript Array has some mutable methods.

Array - JavaScript | MDN

For example, Redux require Immutable Update on your Store implementation.

Object.assign or object spread({ ...object }) can realize immutable updating for Object. But, immutale updating on Array is difficult.

Immutable Update Patterns Â· Redux

Of course, Immutable.js is useful. But Immutable.js is very large library.

So, I want to get minimal and easy to use library.

`@immutable-array/prototype`

@immutable-array/prototype includes immutable version of theses Array.prototype methods.

npm install @immutable-array/prototype

Or, If you want to a single method, you can use a method as independent package.

npm install @immutable-array/pop
npm install @immutable-array/push
npm install @immutable-array/shift
npm install @immutable-array/unshift
npm install @immutable-array/sort
npm install @immutable-array/reverse
npm install @immutable-array/fill
npm install @immutable-array/splice
npm install @immutable-array/copy-within

Example

This library provide same API and behavior without first argument.

import {
  sort,
  unshift,
  push,
  fill,
  splice,
  pop,
  reverse,
  copyWithin,
  shift
} from '@immutable-array/prototype';
describe('prototype', () => {
  it('shift', () => {
    assert.deepStrictEqual(shift(['a', 'b', 'c', 'd', 'e']), [
      'b',
      'c',
      'd',
      'e'
    ]);
  });
  it('unshift', () => {
    assert.deepStrictEqual(unshift(['a', 'b', 'c', 'd', 'e'], 'x'), [
      'x',
      'a',
      'b',
      'c',
      'd',
      'e'
    ]);
  });
  it('pop', () => {
    assert.deepStrictEqual(pop(['a', 'b', 'c', 'd', 'e']), [
      'a',
      'b',
      'c',
      'd'
    ]);
  });
  it('push', () => {
    assert.deepStrictEqual(push(['a', 'b', 'c', 'd', 'e'], 'x'), [
      'a',
      'b',
      'c',
      'd',
      'e',
      'x'
    ]);
  });
  it('splice', () => {
    assert.deepStrictEqual(splice(['a', 'b', 'c', 'd', 'e'], 0, 1, 'x'), [
      'x',
      'b',
      'c',
      'd',
      'e'
    ]);
  });
  it('sort', () => {
    assert.deepStrictEqual(sort(['e', 'a', 'c', 'b', 'd']), [
      'a',
      'b',
      'c',
      'd',
      'e'
    ]);
  });
  it('reverse', () => {
    assert.deepStrictEqual(reverse(['a', 'b', 'c', 'd', 'e']), [
      'e',
      'd',
      'c',
      'b',
      'a'
    ]);
  });
  it('fill', () => {
    assert.deepStrictEqual(fill(new Array(5), 'x'), ['x', 'x', 'x', 'x', 'x']);
  });
  it('copyWithin', () => {
    assert.deepStrictEqual(copyWithin(['a', 'b', 'c', 'd', 'e'], 0, 3, 4), [
      'd',
      'b',
      'c',
      'd',
      'e'
    ]);
  });
});

Use Case

Faao that is GitHub Issue application use @immutable-array/prototype for creating domain model.
Faao apply DDD/CQRS pattern using Almin. Immutable domain model help to work application in safety.

Policy

@immutable-array/prototype has a support policy.

Do

Provide immutable version of Array.prototype method
Provide each method as an module
- For exaple, import push from "@immutable-array/push"
- All prototype method: import { push } from "@immutable-array/prototype"
ECMAScript compatible API without first arguments

For example, @immutable-array/* method should return same result with native API.

import { splice } from '@immutable-array/splice';
var array = [1, 2, 3];
// immutable
var resultArray = splice(array, -1, 1, 'x');
// native
array.splice(-1, 1, 'x');
assert.deepStrictEqual(array, resultArray);

Do not

Should not add non-standard method in ECMAScript
- For example, It does not provide update, delete, merge methods.
Each method should not depended on other method

Finally

Pull requests and stars are always welcome :)

https://github.com/azu/immutable-array-prototype

Get immutable versions of Array methods