Why calling a function in generator runs faster?

Question

function* test() {
  console.time("function-call")
  loop();
  console.timeEnd("function-call");

  console.time("in-function");
  var i, j;
  i = 0;
  while (i < 10000) {
    j = 0;
    while (j < 10000) {
      j++
    }
    i++;
  }
  console.timeEnd("in-function");
}

function loop() {
  var i, j;
  i = 0;
  while (i < 10000) {
    j = 0;
    while (j < 10000) {
      j++
    }
    i++;
  }
}

test().next();

I copied the code block in the 'loop', and pasted into 'test' function to compare time.

function-call: 84ms 
in-function: 596ms

calling a function is much faster than looping inside the function. Why is that so?

Answer 1

@Cristian Traìna Node does not allow to skip empty loops. These optimizations are allowed only in compiled languages like Pascal or C/C++ with flags like -O2.

For this program

var max=process.argv[2];
for(var i=0;i<=max;i++){} // with let results is the same

We can get the following dependency of time of execution from a number of loops. It is a LogLog chart. The first flat area it domain when dominating part of execution time is starting of NodeJs. After 1M loops, you can see that increasing number of iteration scaling with time linearly. Highest measurement takes about 1000 seconds so definitely, V8 does not skip the empty loop.

_{(source: gustawdaniel.pl)}

Coming back to script from question:

• Chrome 71.0.3578.98

function-call: 154.878662109375ms
in-function: 153.7490234375ms

• Node v10.15.0

function-call: 154.183ms
in-function: 152.907ms

• Firefox Quantum 64.0

function-call: 156 ms debugger eval code:4:3
in-function: 1519 ms

• Chromium 71.0.3578.98

function-call: 158.954345703125ms
in-function: 153.663818359375ms

• Vivaldi 2.2

function-call: 153.548095703125ms
in-function: 153.755126953125ms

• Opera 58.0.3135.47

function-call: 154.34814453125ms
in-function: 154.729248046875ms

The computer of my Friend tests:

• Edge

function-call: 3 496,6 ms
in-function: 2 330,9 ms

• Chrome

function-call: 70.69580078125ms
in-function: 70.43310546875ms

So now it seems to be a problem with Firefox and Edge.

Any of these browsers except Firefox and Edge uses V8 engine. Firefox is described here:

https://www.digitaltrends.com/web/mozilla-firefox-new-browser-engine-quantum-2017/

and uses Quantum Flow:.

Edge team think about adopting Chromium engine

https://www.pcmag.com/news/365345/microsofts-edge-browser-to-adopt-googles-chromium-engine

From this article

https://blog.mozilla.org/blog/2018/12/06/goodbye-edge/

We can see that only Chromium from Google and Gecko Quantum from Mozilla will be supported in the future.

If anyone has access to Safari or Edge, please append tests.