Why are setTimeout and setInterval working differently in the browser and in Node.js?

Question

let cnt=0;

let i = setInterval(() => {
  console.log(cnt++);
},200)

setTimeout(() => {
  clearInterval(i);
},2000);

When executed in browser this code logs:- 0 1 2 3 4 5 6 7 8 9

But when executed using Node it logs:- 0 1 2 3 4 5 6 7 8

What is the reason for this?

Answer 1

This is because Chrome does self-correct the drift in setInterval. node (and other browsers) don't. Note that currently specs agree with node, even if there is an active discussion to follow Chrome's behavior.

So in Chrome, it's like if you had a precise

at beginTime + 200
  do fn
at beginTime + 400
  do fn
at beginTime + 600
  do fn
...etc

while in others it will be

at beginTime + 200
  do fn
  at now + 200
    do fn
    ...etc.

But we know there will always be some delay preventing the timer to fire exactly when scheduled, and so in environments without drift correction, we end up with a now that is later the expected time.

So in Chrome, the setInterval job will be in the queue before the setTimeout one, while in other environments, it will come after, because of the drift, even if infinitesimally small.