All permutations of an array

.babelrc

{
  "presets": [
    "env"
  ],
  "env": {
    "test": {
      "presets": [
        "env"
      ]
    }
  }
}

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package.json

{
  "name": "@laran/gists-permutations-js",
  "version": "1.0.0",
  "description": "All permutations of an array",
  "main": "build/permutations.js",
  "scripts": {
    "build": "babel permutations.js --out-dir build",
    "test": "jest",
    "test:watch": "jest --watchAll"
  },
  "repository": {
    "type": "git",
    "url": "git+ssh://git@gist.github.com/68c763350f594a5a4526af95ec84d4be.git"
  },
  "author": "Laran Evans <laran@laranevans.com> (http://www.laranevans.com/)",
  "license": "MIT",
  "bugs": {
    "url": "https://gist.github.com/68c763350f594a5a4526af95ec84d4be"
  },
  "homepage": "https://gist.github.com/68c763350f594a5a4526af95ec84d4be",
  "dependencies": {
    "@laran/readable-helpers": "^1.0.5"
  },
  "jest": {
    "verbose": true
  },
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-preset-env": "^1.7.0",
    "jest": "^23.6.0",
    "yarn": "^1.9.4"
  }
}

permutations.js

import {isLessThan, isEqualTo, swap, notExists, isNotArray, isString} from '@laran/readable-helpers';

export default class Permutations {

	// permute an array of objects
	static of(a = [], n, permutations = []) {

		if (isString(a)) {
			return Permutations.of(a.split(''), 0, permutations);
		} else {
			if (isNotArray(a)) {
				throw "Only arrays can be permuted";
			}

			if (notExists(n)) { // permute the whole array
				return Permutations.of(a, 0, permutations);
			} else if(isEqualTo(n, a.length - 1)) {
				permutations.push(a.slice()); // copy the array to capture it's state
			} else {
				for (let i = n; isLessThan(i, a.length); i++) {
					swap(a, n, i);
					Permutations.of(a, n + 1, permutations);
					swap(a, n, i);
				}
			}
		}

		return permutations;
	}
}

permutations.spec.js

import Permutations from './permutations';

describe("Permutations", () => {
	it('should permute an array of numbers', () => {
		expect(Permutations.of([1, 2, 3])).toEqual([
			[1, 2, 3],
			[1, 3, 2],
			[2, 1, 3],
			[2, 3, 1],
			[3, 2, 1],
			[3, 1, 2]
		]);
	});

	it('should permute a string', () => {
		expect(Permutations.of('abc')).toEqual([
			['a', 'b', 'c'],
			['a', 'c', 'b'],
			['b', 'a', 'c'],
			['b', 'c', 'a'],
			['c', 'b', 'a'],
			['c', 'a', 'b']
		]);
	});
});