How Can I Measure the Execution Time of a JavaScript Function in Milliseconds?

Measuring Execution Time of a Function

Question:

How do I determine the execution time of a function in milliseconds?

Answer:

Using performance.now()

The performance.now() API provides a high-resolution timestamp representing the time since navigation start. To measure the execution time of a function, follow these steps:

var startTime = performance.now();

doSomething(); // <---- Measured code goes between startTime and endTime

var endTime = performance.now();

console.log(`Call to doSomething took ${endTime - startTime} milliseconds`);

For Node.js, first import the performance class:

const { performance } = require('perf_hooks');

Using console.time

console.time provides a convenient way to measure execution time in the browser. Here's how to use it:

console.time('doSomething');

doSomething(); // <---- The function you're measuring time for

console.timeEnd('doSomething');

Note: The string passed to console.time() and console.timeEnd() must match for the timer to end correctly.

References:

• [MDN documentation on console.time()](https://developer.mozilla.org/en-US/docs/Web/API/console/time)
• [Node.js documentation on performance](https://nodejs.org/api/perf_hooks.html)

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