What does setTimeout return?

I was curious that what does setTimeout return. So I did a quick test:

var thing = setTimeout(function(){},1);

And what surprise me is that it gave me a number. 1351 Each time is different.

So is it really all it returns is a number? So I can actually do this as well?

clearTimeout(1351);

Very confusing...

It's a handle (a unique identifier). When you create a timeout, the JavaScript runtime associates a handle with the timeout you created, and it can identify that timeout by the handle setTimeout() returns. When you run clearTimeout(), it will know what timeout you're talking about by looking at the unique handle you pass in.

It can be an Object, I tested it with node.js:

var sto = setTimeout(
    function(){console.log('ping');}, 
    1000
);

console.log(sto);

The output is:

{ _idleTimeout: 1000,
  _idlePrev:
   { '0': [Function: listOnTimeout],
     _idleNext: [Circular],
     _idlePrev: [Circular],
     msecs: 1000 },
  _idleNext:
   { '0': [Function: listOnTimeout],
     _idleNext: [Circular],
     _idlePrev: [Circular],
     msecs: 1000 },
  _idleStart: 2413359232,
  _onTimeout: [Function],
  _repeat: false,
  domain:
   { domain: null,
     _events: { error: [Function] },
     _maxListeners: undefined,
     members: [] } }

You can think of it as a timerID, which uniquely identify a timer, so that you can reset by clearTimeout(timerID)

it's a task ID (I prefer to think it's a task_ID rather than a Timeout_ID that confuses everyone).

imagine you have to launch a default function : "f_cup_of_tea", that any normal individual would end up needing after 5 minutes on your website. :

tea_Task_ID = window.setTimeout(f_cup_of_tea, (5*60*1000), 15, 2);

like: function f_cup_of_tea(milk_ml, sugar) { .... }

but unfortunatly, with ten second late, a psychadelic user prefer to get something different than the entire world, and choose a bad_tequila...

you must cancel the delicious " f_cup_of_tea " scheduled within five minutes ... fortunately javascript have thinking of this kind of problem and you can use :

window.clearTimeout(tea_Task_ID);

(but it woorks only if " f_cup_of_tea " are not yet started).

next, you can launch :

tequila_Task_ID = window.setTimeout(f_bad_tequila, (5*1000), 0);  // for in 5s, with zero ice...