Check spread operator vs Object.assign performance (with varying key sizes)

javascript-spread-operator-performance.js

// Test object recreate speed on large objects vs small objects
function createObject(propsCount) {
  const obj = {};
  for (let i = 0; i < propsCount; i += 1) {
    obj[`p${i}`] = i;
  }
  return obj;
}

function time(label, fn, iterations) {
  const start = Date.now();
  for (let i = 0; i < iterations; i++) {
    fn();
  }
  const interval = Date.now() - start;
  console.log(label, 'Time taken', interval, 'ms', ' PerIteration', interval * 1000 / iterations, 'µs');
}

function spread(obj) {
  return { ...obj, k: 20 };
}

const k = { k: 20 };
function assign(obj) {
  return Object.assign({}, obj, k);
}

const large = createObject(200);
const small = createObject(50);

const iterations = 10000;
setTimeout(() => {
  time('Large Spread', () => spread(large), iterations);
  time('Small Spread', () => spread(small), iterations);
  time('Large assign', () => assign(large), iterations);
}, 1000);

Object.assign is much faster, specially with higher number of keys