Javascript: measure code execution time online

Using the 'User Timing API' is a modern way of doing this:
http://www.html5rocks.com/en/tutorials/webperformance/usertiming/

One option is

jsperf.com

OR

//works in chrome and firefox
console.time("myCode"); // 'myCode' is the namespace
//execute your code here
console.timeEnd("myCode");

OR

var startTime = window.performance.now();
//execute your code here
console.log(window.performance.now() - startTime);

Below approaches I have found till now:-

Approach 1:-

let start = window.performance.now()
/// Your code goes here
let end = window.performance.now()
console.log(`Component Persing Time: ${end - start} ms`);

Approach 2:-

let start = Date.now()
/// Your code goes here
let end = Date.now()
console.log(`Component Persing Time: ${end - start} ms`);

Approach 3:-

console.time();
// Your code goes here
console.timeEnd();

Any above approches you may proceed but got the same result. Happy coding. :)