remDups.js

function remDups(arr) {
  return arr.reduce((memo, num) => {
    if (memo.numMap[num]) return memo;

    memo.numMap[num] = true;
    memo.noDupArr.push(num);
    return memo;
  }, { noDupArr: [], numMap: {} }).noDupArr;
}

/****************************************/

import { expect } from 'chai';

const testCases = [
  {
    given: [1, 5, 1, 1, 2, 3],
    expected: [1, 5, 2, 3]
  }
];

describe('remDups', () => {
  it('should remove duplicates from an array', () => {
    testCases.forEach(test => {
      expect(test.expected).to.deep.equal(remDups(test.given));
    });
  });
});