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Cancel timout / timer if function called again --- debounce function

I want to create a function that starts a timeout, but if the function is called again, before the timer ends, cancel the original call and start the timer again.
I thought I could do:
function setTimer() {
setTimeout(() => {
// do something
}, 3000)
}
...but that doesn't work, for every time I run setTimer(), it doesn't cancel the original call.
Can anyone point me in the right direction?

setTimeout returns an id you can use to clear that timeout with clearTimeout(). So you can clear the existing timeout at the beginning of your function.
For example if you keep clicking it will keep restarting -- if you don't click it finishes in 2 seconds:
let timerID;
function setTimer() {
console.log("starting/restarting timer")
clearTimeout(timerID)
timerID = setTimeout(() => {
console.log("finished")
}, 2000)
}
<p onclick="setTimer()">click to start</p>

What you want to do is cancel the existing timeout and start it over? You can do this by using cleartimeout
let timeoutFunctionVar = null;
const setTimeoutFunction = () => {
clearTimeout(timeoutFunctionVar)
timeoutFunctionVar = setTimeout(() => {
// do something
}, 3000)
};
setTimeoutFunction()
So every time setTimeoutFunction() gets called, the previous timeout gets reset

I figured this question gets asked frequently, especially for searches triggered by key events, but I couldn't find any.
The basic idea is that you keep the timeout id stateful, so you can clear it on subsequent invocations to the TO setter:
const MS_IN_SEC = 1000;
let old_timeout;
function TO_setter(searchString) {
if (old_timeout)
window.clearTimeout(old_timeout);
old_timeout = window.setTimeout(search, 2 * MS_IN_SEC, searchString);
}
function search(s) {
console.log('search for: %s', s);
}

How to stop a self-called setTimeout() function?

I have a count down function. The function used setTimeout() to repeatedly call itself:
function countDownSendCode(timer) {
if(timer >= 0) {
document.querySelector('#send-code').setAttribute('disabled', true);
document.querySelector('#send-code').innerHTML = timer + 's later resend';
setTimeout(function() {
countDownSendCode(timer - 1);
}, 1000);
} else {
document.querySelector('#send-code').removeAttribute('disabled');
document.querySelector('#send-code').innerHTML = 'Send';
}
}
The document.querySelector('#send-code') is a button used to send code. When a user click the button, he cannot click it again until the count down over.
I added below function to the button's click event to call the count down:
function clickSendCode(ev) {
ev.preventDefault();
countDownSendCode(5); // call the count down here
handleAjaxRequest();
}
In some case, in the handleAjaxRequest(), I need to stop the count down and make the button available immediately.
I can call countDownSendCode(-1) to set the button available, but how can I clear the setTimeout()? Because it called by it self, I cannot get the timeID required by clearTimeout().

You can achieve this functionality as shown in the following code snippet:
// global var serving as a handle to Timer
var _timer;
// call this function to start timer
function StartMyTimer()
{
_timer = setTimeout(function(){ alert("Hello, Timer is Running!"); }, 5000);
}
// call this function to stop timer
function StopMyTimer()
{
clearTimeout(_timer);
}
I would also suggest you to consider a pair of functions: setInterval() and clearInterval() which may simplify the coding of repetitive tasks.
Hope this will help.

I'd suggest not recursively calling countDownSendCode(). Rather just set the timer to the correct number of seconds to begin with, then you can return a ref to the timer and pass it to the ajax handler.

function countDownSendCode(timer) {
if(timer >= 0) {
document.querySelector('#send-code').setAttribute('disabled', true);
document.querySelector('#send-code').innerHTML = timer + 's later resend';
countDownSendCode._timer = setTimeout(function() {
countDownSendCode(timer - 1);
}, 1000);
}
else {
if('stop'===timer){
clearTimeout(countDownSendCode._timer);
}
document.querySelector('#send-code').removeAttribute('disabled');
document.querySelector('#send-code').innerHTML = 'Send';
}
}
modify the countDownSendCode function as above. call it with 'stop' string when you need the button to be available immediately.

Stopping Nested Timeouts in Javascript

I want to execute a piece of arbitrary code and be able to stop it whenever I want. I figured I could do this with setTimeout and then use clearTimeout to stop it. However if the code in the timeout creates it's own timeouts, then those keep executing even after I clear the original.
Example:
var timeoutID = setTimeout(
function(){
console.log("first event can be stopped with clearTimout(timeoutID)");
setTimeout(function(){console.log("but not this one")}, 5000)
}, 5000)
Now one way would be to control the code being executed and make it store the value of any additional timeouts into a global variable and clear them all at once. But is there a better way to do this? And is there a way to do this on arbitrary code?
To clarify, I'm trying to be able to execute any function I want, then stop it whenever I want, even if the function contains timeouts

You can put the inner timeout into a variable too:
var innerTimeout,
timeoutID = setTimeout(
function(){
console.log("first event can be stopped with clearTimout(timeoutID)");
innerTimeout = setTimeout(function(){console.log("but not this one")}, 5000);
}, 5000);

You would have to create an array of timeout IDs such as this:
var timeoutIds = [];
timeoutIds.push(setTimeout(
function(){
console.log("first event can be stopped with clearTimout(timeoutID)");
timeoutIds.push(setTimeout(function(){console.log("but not this one")}, 5000));
}, 5000))
And then to clear:
for (int i = 0; i < timeoutIds.length; i++)
{
clearTimeout(timeoutIds[i]);
}
timeoutIds = [];

You could wrap your timeouts in an object or re use timeoutID for the second timeout.
Wrap in an object:
function Timer(){
var me=this;
this.currentTimerID=setTimeout(function(){
console.log("First timeout");
me.currentTimerID=setTimeout(function(){
console.log("Second timeout");
},100);
},100);
};
Timer.prototype.cancel=function(){
clearTimeout(this.currentTimerID);
};
var t = new Timer();//let this run it's course
setTimeout(function(){t = new Timer()},250);//start timer again
setTimeout(function(){t.cancel();},400);// cancel it after the first timeout
Re use timeoutID:
var timeoutID = setTimeout(
function(){
console.log("first event can be stopped with clearTimout(timeoutID)");
timeoutID=setTimeout(function(){console.log("but not this one")}, 100)
}, 100)
setTimeout(function(){
clearTimeout(timeoutID);
},150);// will not execute the second timeout
One tip: If you're testing code with timeout then don't use such high values as it'll take 10 seconds for your original code to run.

how to fire only the very last setTimeout

window.addEventListener('resize', onResize, false);
function onResize() {
timer = setTimeout(function() {
console.log('fire timer');
}, 1000);
}
Resize event fires super fast. So there will be many timer fire every 1000ms. How to fire only the very last timer?

Clear the timer for each call
var timer;
function onResize() {
clearTimeout(timer);
//...
timer = setTimeout(function() {
console.log('fire timer');
}, 1000);
}
(timer may be null or undefined).

If you're already using underscore.js, you have the debounce method to fill this need:
Creates and returns a new debounced version of the passed function that will postpone its execution until after wait milliseconds have elapsed since the last time it was invoked. Useful for implementing behavior that should only happen after the input has stopped arriving.

How to delay the .keyup() handler until the user stops typing?

I’ve got a search field. Right now it searches for every keyup. So if someone types “Windows”, it will make a search with AJAX for every keyup: “W”, “Wi”, “Win”, “Wind”, “Windo”, “Window”, “Windows”.
I want to have a delay, so it only searches when the user stops typing for 200 ms.
There is no option for this in the keyup function, and I have tried setTimeout, but it didn’t work.
How can I do that?

I use this small function for the same purpose, executing a function after the user has stopped typing for a specified amount of time or in events that fire at a high rate, like resize:
function delay(callback, ms) {
var timer = 0;
return function() {
var context = this, args = arguments;
clearTimeout(timer);
timer = setTimeout(function () {
callback.apply(context, args);
}, ms || 0);
};
}
// Example usage:
$('#input').keyup(delay(function (e) {
console.log('Time elapsed!', this.value);
}, 500));
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<label for="input">Try it:
<input id="input" type="text" placeholder="Type something here..."/>
</label>
How it works:
The delay function will return a wrapped function that internally handles an individual timer, in each execution the timer is restarted with the time delay provided, if multiple executions occur before this time passes, the timer will just reset and start again.
When the timer finally ends, the callback function is executed, passing the original context and arguments (in this example, the jQuery's event object, and the DOM element as this).
UPDATE 2019-05-16
I have re-implemented the function using ES5 and ES6 features for modern environments:
function delay(fn, ms) {
let timer = 0
return function(...args) {
clearTimeout(timer)
timer = setTimeout(fn.bind(this, ...args), ms || 0)
}
}
The implementation is covered with a set of tests.
For something more sophisticated, give a look to the jQuery Typewatch plugin.

If you want to search after the type is done use a global variable to hold the timeout returned from your setTimout call and cancel it with a clearTimeout if it hasn't yet happend so that it won't fire the timeout except on the last keyup event
var globalTimeout = null;
$('#id').keyup(function(){
if(globalTimeout != null) clearTimeout(globalTimeout);
globalTimeout =setTimeout(SearchFunc,200);
}
function SearchFunc(){
globalTimeout = null;
//ajax code
}
Or with an anonymous function :
var globalTimeout = null;
$('#id').keyup(function() {
if (globalTimeout != null) {
clearTimeout(globalTimeout);
}
globalTimeout = setTimeout(function() {
globalTimeout = null;
//ajax code
}, 200);
}

Another slight enhancement on CMS's answer. To easily allow for separate delays, you can use the following:
function makeDelay(ms) {
var timer = 0;
return function(callback){
clearTimeout (timer);
timer = setTimeout(callback, ms);
};
};
If you want to reuse the same delay, just do
var delay = makeDelay(250);
$(selector1).on('keyup', function() {delay(someCallback);});
$(selector2).on('keyup', function() {delay(someCallback);});
If you want separate delays, you can do
$(selector1).on('keyup', function() {makeDelay(250)(someCallback);});
$(selector2).on('keyup', function() {makeDelay(250)(someCallback);});

You could also look at underscore.js, which provides utility methods like debounce:
var lazyLayout = _.debounce(calculateLayout, 300);
$(window).resize(lazyLayout);

Explanation
Use a variable to store the timeout function. Then use clearTimeout() to clear this variable of any active timeout functions, and then use setTimeout() to set the active timeout function again. We run clearTimeout() first, because if a user is typing "hello", we want our function to run shortly after the user presses the "o" key (and not once for each letter).
Working Demo
Super simple approach, designed to run a function after a user has finished typing in a text field...
$(document).ready(function(e) {
var timeout;
var delay = 2000; // 2 seconds
$('.text-input').keyup(function(e) {
$('#status').html("User started typing!");
if(timeout) {
clearTimeout(timeout);
}
timeout = setTimeout(function() {
myFunction();
}, delay);
});
function myFunction() {
$('#status').html("Executing function for user!");
}
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Status: <span id="status">Default Status</span><br>
<textarea name="text-input" class="text-input"></textarea>

Based on the answer of CMS, I made this :
Put the code below after include jQuery :
/*
* delayKeyup
* http://code.azerti.net/javascript/jquery/delaykeyup.htm
* Inspired by CMS in this post : http://stackoverflow.com/questions/1909441/jquery-keyup-delay
* Written by Gaten
* Exemple : $("#input").delayKeyup(function(){ alert("5 secondes passed from the last event keyup."); }, 5000);
*/
(function ($) {
$.fn.delayKeyup = function(callback, ms){
var timer = 0;
$(this).keyup(function(){
clearTimeout (timer);
timer = setTimeout(callback, ms);
});
return $(this);
};
})(jQuery);
And simply use like this :
$('#input').delayKeyup(function(){ alert("5 secondes passed from the last event keyup."); }, 5000);
Careful : the $(this) variable in the function passed as a parameter does not match input

jQuery:
var timeout = null;
$('#input').keyup(function() {
clearTimeout(timeout);
timeout = setTimeout(() => {
console.log($(this).val());
}, 1000);
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.4/jquery.min.js"></script>
<input type="text" id="input" placeholder="Type here..."/>
Pure Javascript:
let input = document.getElementById('input');
let timeout = null;
input.addEventListener('keyup', function (e) {
clearTimeout(timeout);
timeout = setTimeout(function () {
console.log('Value:', input.value);
}, 1000);
});
<input type="text" id="input" placeholder="Type here..."/>

Delay Multi Function Calls using Labels
This is the solution i work with. It will delay the execution on ANY function you want. It can be the keydown search query, maybe the quick click on previous or next buttons ( that would otherwise send multiple request if quickly clicked continuously , and be not used after all). This uses a global object that stores each execution time, and compares it with the most current request.
So the result is that only that last click / action will actually be called, because those requests are stored in a queue, that after the X milliseconds is called if no other request with the same label exists in the queue!
function delay_method(label,callback,time){
if(typeof window.delayed_methods=="undefined"){window.delayed_methods={};}
delayed_methods[label]=Date.now();
var t=delayed_methods[label];
setTimeout(function(){ if(delayed_methods[label]!=t){return;}else{ delayed_methods[label]=""; callback();}}, time||500);
}
You can set your own delay time ( its optional, defaults to 500ms). And send your function arguments in a "closure fashion".
For example if you want to call the bellow function:
function send_ajax(id){console.log(id);}
To prevent multiple send_ajax requests, you delay them using:
delay_method( "check date", function(){ send_ajax(2); } ,600);
Every request that uses the label "check date" will only be triggered if no other request is made in the 600 miliseconds timeframe. This argument is optional
Label independency (calling the same target function) but run both:
delay_method("check date parallel", function(){send_ajax(2);});
delay_method("check date", function(){send_ajax(2);});
Results in calling the same function but delay them independently because of their labels being different

If someone like to delay the same function, and without external variable he can use the next script:
function MyFunction() {
//Delaying the function execute
if (this.timer) {
window.clearTimeout(this.timer);
}
this.timer = window.setTimeout(function() {
//Execute the function code here...
}, 500);
}

This function extends the function from Gaten's answer a bit in order to get the element back:
$.fn.delayKeyup = function(callback, ms){
var timer = 0;
var el = $(this);
$(this).keyup(function(){
clearTimeout (timer);
timer = setTimeout(function(){
callback(el)
}, ms);
});
return $(this);
};
$('#input').delayKeyup(function(el){
//alert(el.val());
// Here I need the input element (value for ajax call) for further process
},1000);
http://jsfiddle.net/Us9bu/2/

I'm surprised that nobody mention the problem with multiple input in CMS's very nice snipped.
Basically, you would have to define delay variable individually for each input. Otherwise if sb put text to first input and quickly jump to other input and start typing, callback for the first one WON'T be called!
See the code below I came with based on other answers:
(function($) {
/**
* KeyUp with delay event setup
*
* #link http://stackoverflow.com/questions/1909441/jquery-keyup-delay#answer-12581187
* #param function callback
* #param int ms
*/
$.fn.delayKeyup = function(callback, ms){
$(this).keyup(function( event ){
var srcEl = event.currentTarget;
if( srcEl.delayTimer )
clearTimeout (srcEl.delayTimer );
srcEl.delayTimer = setTimeout(function(){ callback( $(srcEl) ); }, ms);
});
return $(this);
};
})(jQuery);
This solution keeps setTimeout reference within input's delayTimer variable. It also passes reference of element to callback as fazzyx suggested.
Tested in IE6, 8(comp - 7), 8 and Opera 12.11.

This worked for me where I delay the search logic operation and make a check if the value is same as entered in text field. If value is same then I go ahead and perform the operation for the data related to search value.
$('#searchText').on('keyup',function () {
var searchValue = $(this).val();
setTimeout(function(){
if(searchValue == $('#searchText').val() && searchValue != null && searchValue != "") {
// logic to fetch data based on searchValue
}
else if(searchValue == ''){
// logic to load all the data
}
},300);
});

Delay function to call up on every keyup.
jQuery 1.7.1 or up required
jQuery.fn.keyupDelay = function( cb, delay ){
if(delay == null){
delay = 400;
}
var timer = 0;
return $(this).on('keyup',function(){
clearTimeout(timer);
timer = setTimeout( cb , delay );
});
}
Usage: $('#searchBox').keyupDelay( cb );

From ES6, one can use arrow function syntax as well.
In this example, the code delays keyup event for 400ms after users finish typeing before calling searchFunc make a query request.
const searchbar = document.getElementById('searchBar');
const searchFunc = // any function
// wait ms (milliseconds) after user stops typing to execute func
const delayKeyUp = (() => {
let timer = null;
const delay = (func, ms) => {
timer ? clearTimeout(timer): null
timer = setTimeout(func, ms)
}
return delay
})();
searchbar.addEventListener('keyup', (e) => {
const query = e.target.value;
delayKeyUp(() => {searchFunc(query)}, 400);
})
Updated Typescript version:
const delayKeyUp = (() => {
let timer: NodeJS.Timeout;
return (func: Function, ms: number) => {
timer ? clearTimeout(timer) : null;
timer = setTimeout(() => func(), ms);
};
})();

This is a solution along the lines of CMS's, but solves a few key issues for me:
Supports multiple inputs, delays can run concurrently.
Ignores key events that didn't changed the value (like Ctrl, Alt+Tab).
Solves a race condition (when the callback is executed and the value already changed).
var delay = (function() {
var timer = {}
, values = {}
return function(el) {
var id = el.form.id + '.' + el.name
return {
enqueue: function(ms, cb) {
if (values[id] == el.value) return
if (!el.value) return
var original = values[id] = el.value
clearTimeout(timer[id])
timer[id] = setTimeout(function() {
if (original != el.value) return // solves race condition
cb.apply(el)
}, ms)
}
}
}
}())
Usage:
signup.key.addEventListener('keyup', function() {
delay(this).enqueue(300, function() {
console.log(this.value)
})
})
The code is written in a style I enjoy, you may need to add a bunch of semicolons.
Things to keep in mind:
A unique id is generated based on the form id and input name, so they must be defined and unique, or you could adjust it to your situation.
delay returns an object that's easy to extend for your own needs.
The original element used for delay is bound to the callback, so this works as expected (like in the example).
Empty value is ignored in the second validation.
Watch out for enqueue, it expects milliseconds first, I prefer that, but you may want to switch the parameters to match setTimeout.
The solution I use adds another level of complexity, allowing you to cancel execution, for example, but this is a good base to build on.

Combining CMS answer with Miguel's one yields a robust solution allowing concurrent delays.
var delay = (function(){
var timers = {};
return function (callback, ms, label) {
label = label || 'defaultTimer';
clearTimeout(timers[label] || 0);
timers[label] = setTimeout(callback, ms);
};
})();
When you need to delay different actions independently, use the third argument.
$('input.group1').keyup(function() {
delay(function(){
alert('Time elapsed!');
}, 1000, 'firstAction');
});
$('input.group2').keyup(function() {
delay(function(){
alert('Time elapsed!');
}, 1000, '2ndAction');
});

Building upon CMS's answer here's new delay method which preserves 'this' in its usage:
var delay = (function(){
var timer = 0;
return function(callback, ms, that){
clearTimeout (timer);
timer = setTimeout(callback.bind(that), ms);
};
})();
Usage:
$('input').keyup(function() {
delay(function(){
alert('Time elapsed!');
}, 1000, this);
});

If you want to do something after a period of time and reset that timer after a specific event like keyup, the best solution is made with clearTimeout and setTimeout methods:
// declare the timeout variable out of the event listener or in the global scope
var timeout = null;
$(".some-class-or-selector-to-bind-event").keyup(function() {
clearTimeout(timout); // this will clear the recursive unneccessary calls
timeout = setTimeout(() => {
// do something: send an ajax or call a function here
}, 2000);
// wait two seconds
});

Use
mytimeout = setTimeout( expression, timeout );
where expression is the script to run and timeout is the time to wait in milliseconds before it runs - this does NOT hault the script, but simply delays execution of that part until the timeout is done.
clearTimeout(mytimeout);
will reset/clear the timeout so it does not run the script in expression (like a cancel) as long as it has not yet been executed.

Based on the answer of CMS, it just ignores the key events that doesn't change value.
var delay = (function(){
var timer = 0;
return function(callback, ms){
clearTimeout (timer);
timer = setTimeout(callback, ms);
};
})();
var duplicateFilter=(function(){
var lastContent;
return function(content,callback){
content=$.trim(content);
if(content!=lastContent){
callback(content);
}
lastContent=content;
};
})();
$("#some-input").on("keyup",function(ev){
var self=this;
delay(function(){
duplicateFilter($(self).val(),function(c){
//do sth...
console.log(c);
});
}, 1000 );
})

User lodash javascript library and use _.debounce function
changeName: _.debounce(function (val) {
console.log(val)
}, 1000)

Use the bindWithDelay jQuery plugin:
element.bindWithDelay(eventType, [ eventData ], handler(eventObject), timeout, throttle)

var globalTimeout = null;
$('#search').keyup(function(){
if(globalTimeout != null) clearTimeout(globalTimeout);
globalTimeout =setTimeout(SearchFunc,200);
});
function SearchFunc(){
globalTimeout = null;
console.log('Search: '+$('#search').val());
//ajax code
};

Here is a suggestion I have written that takes care of multiple input in your form.
This function gets the Object of the input field, put in your code
function fieldKeyup(obj){
// what you want this to do
} // fieldKeyup
This is the actual delayCall function, takes care of multiple input fields
function delayCall(obj,ms,fn){
return $(obj).each(function(){
if ( typeof this.timer == 'undefined' ) {
// Define an array to keep track of all fields needed delays
// This is in order to make this a multiple delay handling
function
this.timer = new Array();
}
var obj = this;
if (this.timer[obj.id]){
clearTimeout(this.timer[obj.id]);
delete(this.timer[obj.id]);
}
this.timer[obj.id] = setTimeout(function(){
fn(obj);}, ms);
});
}; // delayCall
Usage:
$("#username").on("keyup",function(){
delayCall($(this),500,fieldKeyup);
});

Take a look at the autocomplete plugin. I know that it allows you to specify a delay or a minimum number of characters. Even if you don't end up using the plugin, looking through the code will give you some ideas on how to implement it yourself.

Well, i also made a piece of code for limit high frequency ajax request cause by Keyup / Keydown. Check this out:
https://github.com/raincious/jQueue
Do your query like this:
var q = new jQueue(function(type, name, callback) {
return $.post("/api/account/user_existed/", {Method: type, Value: name}).done(callback);
}, 'Flush', 1500); // Make sure use Flush mode.
And bind event like this:
$('#field-username').keyup(function() {
q.run('Username', this.val(), function() { /* calling back */ });
});

Saw this today a little late but just want to put this here in case someone else needed. just separate the function to make it reusable. the code below will wait 1/2 second after typing stop.
var timeOutVar
$(selector).on('keyup', function() {
clearTimeout(timeOutVar);
timeOutVar= setTimeout(function(){ console.log("Hello"); }, 500);
});

// Get an global variable isApiCallingInProgress
// check isApiCallingInProgress
if (!isApiCallingInProgress) {
// set it to isApiCallingInProgress true
isApiCallingInProgress = true;
// set timeout
setTimeout(() => {
// Api call will go here
// then set variable again as false
isApiCallingInProgress = false;
}, 1000);
}