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snippets/js/s/hz.md

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+---
+title: Hertz frequency of function
+type: snippet
+language: javascript
+tags: [function]
+unlisted: true
+cover: lake-runner
+dateModified: 2021-01-04T13:04:15+02:00
+---
+
+Measures the number of times a function is executed per second (hz/hertz).
+
+- 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.
+
+```js
+const hz = (fn, iterations = 100) => {
+  const before = performance.now();
+  for (let i = 0; i < iterations; i++) fn();
+  return (1000 * iterations) / (performance.now() - before);
+};
+```
+
+```js
+const numbers = Array(10000).fill().map((_, i) => i);
+
+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;
+};
+
+Math.round(hz(sumReduce)); // 572
+Math.round(hz(sumForLoop)); // 4784
+```