Javascript get function execution time

time-method-call.js

// Taken from
// http://calendar.perfplanet.com/2014/performance-measurements-using-chrome-devtools-code-snippets/

var primesApp = {
  findFirstPrimes: function () {
    var n = Number(document.querySelector('#n').value);
    console.log('finding first', n, 'primes');
    var primes = findFirstPrimes(n);
    renderPrimes(primes);
  }
};
document.addEventListener('DOMContentLoaded', function() {
  document.querySelector('#find').addEventListener('click', function () {
    primesApp.findFirstPrimes();
  });
});

(function timeMethodCall() {
  var object = primesApp;
  var methodName = 'findFirstPrimes';
  var originalMethod = object[methodName];
  console.assert(typeof originalMethod === 'function', 'cannot find method ' + methodName);
  object[methodName] = function () {
    console.time(methodName);
    originalMethod.call(object);
    console.timeEnd(methodName);
    // restore original methodName
    object[methodName] = originalMethod;
  };
}());