30秒学会 JavaScript 片段 – 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 performance.now() to get the difference in milliseconds before and after the iteration loop to calculate the time elapsed executing the function iterations times.
Return the number of cycles per second by converting milliseconds to seconds and dividing it by the time elapsed.
Omit the second argument, iterations, to use the default of 100 iterations.

代码片段

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

使用样例

// 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