# JavaScript: Get the number of times a function executed per second

## JavaScript fundamental (ES6 Syntax): Exercise-218 with Solution

Write a JavaScript program to get 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.

**Sample Solution:**

**JavaScript Code:**

```
//#Source https://bit.ly/2neWfJ2
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
console.log(Math.round(hz(sumReduce)));
console.log(Math.round(hz(sumForLoop)));
```

Sample Output:

3584 2688

**Flowchart:**

**Live Demo: **

See the Pen javascript-fundamental-exercise-218 by w3resource (@w3resource) on CodePen.

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