30-seconds-of-code/snippets/hz.md

hz

Returns the number of times a function executed per second. hz is the unit for hertz, the unit of frequency defined as one cycle per second.

Use window.performance.now() before and after the iteration loop to get the difference in milliseconds to calculate the time elapsed executing the function iterations times, using math to calculate the number of iterations per second. Omit the second argument, iterations, to use the default of 100 iterations.

const hz = (fn, iterations = 100) => {
  const before = performance.now();
  for (let i = 0; i < iterations; i++) fn();
  return 1000 * iterations / (performance.now() - before);
};

// 10,000 element array
const numbers = Array(10000).fill().map((_, i) => i);

// Test functions with the same goal: sum up the elements in the array
const sumReduce = () => numbers.reduce((acc, n) => acc + n, 0);
const sumForLoop = () => {
  let sum = 0
  for (let i = 0; i < numbers.length; i++) sum += numbers[i]
  return sum
};

// `sumForLoop` is nearly 10 times faster
Math.round(hz(sumReduce)); // 572
Math.round(hz(sumForLoop)); // 4784