let strings = [];
numbers = [];
for (let i = 0; i < 1000000; i++) {
  strings.push(`${i}`.repeat(100));
  numbers.push(i);
}

(() => {
  console.time('numbers');

  const result = {};

  for (number of numbers) {
    result[number] = 1;
  }
  console.timeEnd('numbers');
})();

(() => {
  console.time('strings');
  const result = {};
  for (string of strings) {
    result[string] = 1;
  }
  console.timeEnd('strings');
})();