How to time different parts of a loop in Javascript

Question

Not a duplicate of How to measure time taken by a function to execute. Please actually read my question before marking it as a duplicate of something else. Regardless, it's been answered.

I have code like

for (var i = 0 ; i < 10000 ; i++) {

    doSomething();

    doSomethingElse();

}

And I want to know how much time each function inside the loop is taking overall. How do I measure that?

You can check the used time on devtools Performance tab. – Teemu Jul 07 '17 at 07:42 — Teemu, Jul 07 '17 at 07:42

Vineesh · Accepted Answer · 2017-07-07T08:21:38.380

1

var t1;
var t2;
var f1Time =0;
var f2Time =0;
for (var i = 0 ; i < 10000 ; i++) {
    t1 = performance.now();
    doSomething();
    t2  = performance.now();
    f1Time+= (t2 - t1);

    t1 = performance.now();
    doSomethingElse();
    t2  = performance.now();
    f1Time+=(t2 - t1);

}

edited Jul 07 '17 at 08:21

answered Jul 07 '17 at 07:34

Vineesh

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Except that you would use `performance.now()`. – Sebastian Simon Jul 07 '17 at 07:43
Yes, that would be more accurate. I updated the answer. Thanks – Vineesh Jul 07 '17 at 07:45
That doesn't work. That just gives me the total time taken by the for loop. – Isaac King Jul 07 '17 at 08:18
Then you should keep the time inside the loop. Updated the answer – Vineesh Jul 07 '17 at 08:19

score 0 · Answer 2 · answered Jul 07 '17 at 07:43

Create a test object and register the individual time differences:

function doSomething() {
  t = Date.now();
  while (Date.now() < t + 13) {}
}

function doSomethingElse() {
  t = Date.now();
  while (Date.now() < t + 27) {}
}
var tests = {
  "doSomething": [],
  "doSomethingElse": []
};
for (var i_1 = 0; i_1 < 10; i_1++) {
  var t = Date.now();
  doSomething();
  tests.doSomething.push(Date.now() - t);
  t = Date.now();
  doSomethingElse();
  tests.doSomethingElse.push(Date.now() - t);
}
for (var key in tests) {
  if (tests.hasOwnProperty(key)) {
    tests[key] = tests[key]
      .reduce(function(sum, value) {
        return sum + value;
      }, 0);
  }
}
console.log(tests);

How to time different parts of a loop in Javascript

2 Answers2