A quick JavaScript function performance test on the browser console

function-performance-test.js

var i = performance.now();
yourFunction();
performance.now() - i;
 
//Or make a helper function, like this:
function performanceTest(testFunction, iterations) {
  'use strict';
  var sum = 0;
  var start = performance.now();
  for (var i = 0; i < iterations; i++) {
    testFunction();
  }
  var time=performance.now() - start;
  return time;
}
 
//And use it like this:
performanceTest(function(){
  Math.random()*Math.random();
}, 1000);
 
//In NodeJS you would need to use process.hrtime() instead of performance.now() and it behaves a little differently.