Create hz.md

snippets/hz.md

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+### 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.
+
+```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
+// 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
+```