Here's a link with some sample code.

/

I assumed, until I started testing, that the return value of a setTimeout() would be some kind of browser object.

In fact it seems to be a simple integer. I also believed that assigning the return value of setTimeout to a global variable would mean that there could only be one such object. But as you'll see if you click the "start timer" button more than one, there can be multiple timers running concurrently.

For instance

• I click the start button
• the script creates a timeout
• it is timeout 1, due to fire in five seconds
• one second later, I click again and now there's a timeout 2
• now I have timeout 1 due to fire in four seconds and timeout 2 in five seconds
• I click the stop button and only timeout 2 is cleared

The problem of user clicks creating multiple timers can be solved by always clearing the current timeout var before setting it. But I would really like to understand what Javascript is doing actually doing here.

Here's a link with some sample code.

http://jsfiddle/4djNt/2/

I assumed, until I started testing, that the return value of a setTimeout() would be some kind of browser object.

In fact it seems to be a simple integer. I also believed that assigning the return value of setTimeout to a global variable would mean that there could only be one such object. But as you'll see if you click the "start timer" button more than one, there can be multiple timers running concurrently.

For instance

• I click the start button
• the script creates a timeout
• it is timeout 1, due to fire in five seconds
• one second later, I click again and now there's a timeout 2
• now I have timeout 1 due to fire in four seconds and timeout 2 in five seconds
• I click the stop button and only timeout 2 is cleared

The problem of user clicks creating multiple timers can be solved by always clearing the current timeout var before setting it. But I would really like to understand what Javascript is doing actually doing here.

• javascript
• settimeout
• dom-events

Share Improve this question Follow edited Apr 10, 2020 at 8:12 Brian Tompsett - 汤莱恩 5,8937272 gold badges6161 silver badges133133 bronze badges asked Oct 26, 2012 at 2:11 AmbroseChapelAmbroseChapel 12.1k77 gold badges4949 silver badges6969 bronze badges 4

• 1 "But I would really like to understand what Javascript is doing actually doing here." --- you have explained it in your "For instance" list – zerkms Commented Oct 26, 2012 at 2:13
• 1 The return value is sort of like a timer ID. To stop a particular timer, you run clearTimeout(id). – Blender Commented Oct 26, 2012 at 2:13
• 1 From MDN "timeoutID is the numerical ID of the timeout, which can be used later with window.clearTimeout". When you assign it to the same global var, you are just overwriting the value – Phil Commented Oct 26, 2012 at 2:13
• Imagine having an array [...] of all the timeouts. To access each one of them, JavaScript needs an ID, or the index of the timeout in the array. – JCOC611 Commented Oct 26, 2012 at 2:14

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 5

setTimeout and setInterval return a number. The number is the id of the timer. Active timers can be stopped using clearTimeout and clearInterval respectively.

If you lose the timer's id, you'd either have to guess it again, or wait for it to plete (assuming it's a timeout).

If the timer hasn't been cancelled in the number of milliseconds specified in the delay parameter, it will execute the callback function in the global context.

The return value of setTimeout can be passed to clearTimeout to prevent a scheduled task from running. If the variable has been set and your button is pushed again, run clearTimeout first, then setTimeout assuming you want only the 2nd push to schedule.

The questioner asks only about timeout objects, which are returned in lieu of numbers in some environments, for instance timeoutObject. For purposes of canceling the callback, passing the entire timeout object to clearTimeout(toObj) does the trick.

{
  called : bool
  _idleTimeout : null
  _idlePrev : null
  _idleNext : null
  _idleStart : null
  _onTimeout : function (){}
  _repeat : null
  unref : function () {}
  ref : function () {}
  close : function () {}
}