const array = [];
for (let i = 0; i < 1E7; ++i)
  array.push(i);


/* Set-based.
 */
const optionA = () => [...new Set(array)];


/* Push to new array, O(1) membership tests.
 */
const optionB = () => {
  const unique = [];
  const inUnique = {};
  for (let i = 0; i < array. length; ++i) {
    const el = array[i];
    if (inUnique[el] !== true) {
      unique.push(el);
      inUnique[el] = true;
    }
  }
  return unique;
};


/* Push to new array, O(n) membership tests.
 * (Will be way too slow for large, unrestricted arrays)
 */
const optionC = () => {
  const unique = [];
  for (let i = 0; i < array. length; ++i) {
    const el = array[i];
    if (unique.indexOf(el) === -1)
      unique.push(el);
  }
  return unique;
};


const benchmark = f => {
  console.log(f);
  for (let i = 0; i < 5; ++i) {
    const tPreMs = Date.now();
    f();
    const tSpentMs = Math.round(Date.now() - tPreMs);
    console.log(tSpentMs);
  }
  console.log();
};


benchmark(optionA);
benchmark(optionB);
benchmark(optionC);