Check if a timeout has been cleared?

Question

I am wondering is there a way to tell if a timeout is still set

var t=setTimeout("alertMsg()",3000);

I thought t would be like undefined when you clear it. But it seems to have some id that does not get cleared.

Answer 1

Not directly, but you can create a wrapper object to give that functionality. A rough implementation is like so:

function Timeout(fn, interval) {
    var id = setTimeout(fn, interval);
    this.cleared = false;
    this.clear = function () {
        this.cleared = true;
        clearTimeout(id);
    };
}

Then you can do something like:

var t = new Timeout(function () {
    alert('this is a test');
}, 5000);
console.log(t.cleared); // false
t.clear();
console.log(t.cleared); // true

Answer 2

First of all, I am giving credit to Reid for portions of this answer, however I felt that I should add some suggestions. With my slight additions to Reid's code, this will:

• auto-clear when the timeout naturally expires
• optionally set the scope of the timeout function (rather than just executing in global scope).
• optionally pass arguments array to the timeout function

here it is:

function Timeout(fn, interval, scope, args) {
    scope = scope || window;
    var self = this;
    var wrap = function(){
        self.clear();
        fn.apply(scope, args || arguments);
    }
    this.id = setTimeout(wrap, interval);
}
Timeout.prototype.id = null
Timeout.prototype.cleared = false;
Timeout.prototype.clear = function () {
    clearTimeout(this.id);
    this.cleared = true;
    this.id = null;
};

[begin comment-free plug] Oh, and I am using the prototype model of adding methods to classes, but only because I prefer it, not because I feel it is more correct [end comment-free plug]

Answer 3

Just set t to 0 in your timeout function:

t = 0;

If you use clearTimeout it sets the timeout id to 0, so checking for t === 0 will check if it's either been cleared or completed.

Answer 4

No. In order to know, you'll need to null the t variable after you call clearTimeout. Otherwise there's really no indicator.

And FYI, it's better to pass a direct reference to the function instead of a string that will be eval'd.

var t=setTimeout(alertMsg,3000);

Answer 5

Like some users suggests in comments, whenever the timeout is either triggered (after the set time has passed) or cleared with clearTimeout, set it manually to false or preferably null. Then you can perform a simple if-check to see if it is active. Also remember to initialize it as false/null if needed.

Created a small test page for this: https://codepen.io/TheJesper/pen/rJzava

Answer 6

this is only relevant for node.js: setTimeout returns an object, which has the _destroyed property

Welcome to Node.js v18.12.1.
Type ".help" for more information.
> let x = setTimeout(function(){},60000)
undefined
> x
Timeout {
  _idleTimeout: 60000,
  _idlePrev: [TimersList],
  _idleNext: [TimersList],
  _idleStart: 2170,
  _onTimeout: [Function (anonymous)],
  _timerArgs: undefined,
  _repeat: null,
  _destroyed: false,
  [Symbol(refed)]: true,
  [Symbol(kHasPrimitive)]: false,
  [Symbol(asyncId)]: 27,
  [Symbol(triggerId)]: 5
}
> x._destroyed
false
> clearTimeout(x)
undefined
> x._destroyed
true
> 

note: _destroyed is also true if the event has fired

> let y = setTimeout(function(){console.log("yay");},10)
undefined
> yay
> y
Timeout {
  _idleTimeout: 10,
  _idlePrev: null,
  _idleNext: null,
  _idleStart: 198348,
  _onTimeout: [Function (anonymous)],
  _timerArgs: undefined,
  _repeat: null,
  _destroyed: true,
  [Symbol(refed)]: true,
  [Symbol(kHasPrimitive)]: false,
  [Symbol(asyncId)]: 508,
  [Symbol(triggerId)]: 5
}

Answer 7

There is another way to check a presence of the timeout. Value which holds a timeout has for default a number value which is increasing with time. So we can do next in "if" construction:

if (someBooleanValue && !parseInt(@changeToCriteriaTimeout) > 0){
  //Do something
}