Does the browser keep track of active timer IDs? - javascript

Does the browser keep track of active setInterval and setTimeout IDs? Or is this solely up to the developer to keep track of?
If it does keep track of them, is it accessible via the BOM?

It is up for the developer to keep track of. You can do so by using the returned value of the setTimeout/setInterval function and passing that value to the clearTimeout/clearInterval function - as described in other answers here.
This appears to be because each browser will implement keeping track of the intervals in their own way.
From w3.org/TR/2009/WD-html5-20090212/no.html (a draft, but w3schools and http://w3.org/TR/Window explain it almost the same way) - setTimeout and setInterval return a long and clearTimeout/clearInterval accept a long to find and cancel

You can add such global timers tracking by overriding the setTimeout/seInterval functions. As a bonus you easily add code when a timer is set or popped, track live timers or popped timers, etc...
For example:
timers = {}; // pending timers will be in this variable
originalSetTimeout = window.setTimeout;
// override `setTimeout` with a function that keeps track of all timers
window.setTimeout = function(fu, t) {
var id = originalSetTimeout(function() {
console.log(id+" has timed out");
delete timers[id]; // do not track popped timers
fu();
}, t);
// track this timer in the `timers` variable
timers[id] = {id:id, setAt: new Date(), timeout: t};
console.log(id+" has been set to pop in "+t+"ms");
}
// from this point onward all uses of setTimeout will be tracked, logged to console and pending timers will be kept in the global variable "timers".

This may interest you, if you are curious about how the timer is 'remembered' by its window.
<!doctype html>
<html lang= "en">
<head>
<meta charset= "utf-8">
<title>Timer </title>
</head>
<body>
<h1>Timers</h1>
<script>
if(!window.timers){
var timers= [], i= 0;
while(i<5){
timers.push(setInterval(function(){
if(confirm(timers.join('\n')+'\nRemove a timer?')){
clearInterval(timers.shift());
}
},
i*1000+1000));
++i;
}
}
</script>
</body>
</html>

Update:
There are 2 aspects to this question.
Does the browser keep track of timer IDs?
Are they accessible
I can only presume for #1 (and later #2) that the OP means "are they tracked" in the general sense because as a Developer s/he would like control over them.
In short, yes they are tracked (as #s_hewitt noted, as long values by the browser) and they can be managed by the developer by maintaining a reference to the timers when setup.
As a developer you can control (e.g. stop) them by calling (clearInterval(handleRef), or clearTimeout(handleRef))
However there is no default window.timers or similar collection that gives you a list of the existing timers - you will need to maintain that yourself if you feel you need to.
function startPolling(delay){
pollHandle = setInterval(doThis, delay);
}
function stopPolling(){
clearInterval(pollHandle);
}
function doThisIn30minUnlessStopped(){
timerHandle = setTimeout(doThisThing, 1800000);
}
function stop30minTimer(){
clearTimeout(timerHandle);
}
You simply need to create a variable reference to your timer, and if/when needed, clear it by name.
When you load another page, all the timers are automatically cleared by the browser so you don't need to maintain a handle, and clear them unless you need/want to.

Look at the scripts below, the browser could remember the id of each setTimeout iteration
for (i = 1; i <= d; i++) {
(function(j) {
var delay = j/d;
t[j] = setTimeout(function() {
elem.style.top = j+"px";
},delay);
})(i);
}
You can access them by
for (i in t) {
alert(t[i]);
}

Related

Chrome-extension:Can the script run separately even when the page is not active? [duplicate]

When events are queued with setTimeout/setInterval, and the user is viewing a separate tab, Chrome and Firefox enforce a minimum 1000ms lag before the event is executed. This article details the behaviour.
This has been discussed on StackOverflow previously, but the questions and answers only applied to animations. Obviously, an animation can just be forced to update to the latest state when a user re-enters the tab.
But the solution does not work for sequenced audio. I have Web Audio API playing several audio files in sequence, and setTimeout is used to countdown to when the next audio file plays. If you put the tab in the background, you get an annoying 1 second gap between each pattern -- an extreme flaw in an API designed for advanced audio.
You can witness this behaviour in various HTML5 sequencers, e.g. with PatternSketch -- just by entering a pattern, playing, and going to another tab.
So I'm in need of a workaround: a way to queue events without the 1000ms clamp. Does anyone know of a way?
The only solution I can think of is to have window.postMessage run every single millisecond and check each time if the event is to execute. That is definitely detrimental to performance. Is this the only option?
Apparently there is no event system planned for Web Audio API, so that is out of question.
EDIT: Another answer is to use WebWorkers per https://stackoverflow.com/a/12522580/1481489 - this answer is a little specific, so here's something more generic:
interval.js
var intervalId = null;
onmessage = function(event) {
if ( event.data.start ) {
intervalId = setInterval(function(){
postMessage('interval.start');
},event.data.ms||0);
}
if ( event.data.stop && intervalId !== null ) {
clearInterval(intervalId);
}
};
and your main program:
var stuff = { // your custom class or object or whatever...
first: Date.now(),
last: Date.now(),
callback: function callback() {
var cur = Date.now();
document.title = ((cur-this.last)/1000).toString()+' | '+((cur-this.first)/1000).toString();
this.last = cur;
}
};
var doWork = new Worker('interval.js');
doWork.onmessage = function(event) {
if ( event.data === 'interval.start' ) {
stuff.callback(); // queue your custom methods in here or whatever
}
};
doWork.postMessage({start:true,ms:250}); // tell the worker to start up with 250ms intervals
// doWork.postMessage({stop:true}); // or tell it just to stop.
Totally ugly, but you could open up a child popup window. However, all this does is transfer some of the caveats to the child window, i.e. if child window is minimized the 1000ms problem appears, but if it is simply out of focus, there isn't an issue. Then again, if it is closed, then it stops, but all the user has to do is click the start button again.
So, I suppose this doesn't really solve your problem... but here's a rough draft:
var mainIntervalMs = 250;
var stuff = { // your custom class or object or whatever...
first: Date.now(),
last: Date.now(),
callback: function callback(){
var cur = Date.now();
document.title = ((cur-this.last)/1000).toString()+' | '+((cur-this.first)/1000).toString();
this.last = cur;
}
};
function openerCallbackHandler() {
stuff.callback(); // queue your custom methods in here or whatever
}
function openerTick(childIntervalMs) { // this isn't actually used in this window, but makes it easier to embed the code in the child window
setInterval(function() {
window.opener.openerCallbackHandler();
},childIntervalMs);
}
// build the popup that will handle the interval
function buildIntervalWindow() {
var controlWindow = window.open('about:blank','controlWindow','width=10,height=10');
var script = controlWindow.document.createElement('script');
script.type = 'text/javascript';
script.textContent = '('+openerTick+')('+mainIntervalMs+');';
controlWindow.document.body.appendChild(script);
}
// write the start button to circumvent popup blockers
document.write('<input type="button" onclick="buildIntervalWindow();return false;" value="Start" />');
I'd recommend working out a better way to organize, write, etc. but at the least it should point you in the right direction. It should also work in a lot of diff browsers (in theory, only tested in chrome). I'll leave you to the rest.
Oh, and don't forget to build in auto-closing of the child window if the parent drops.

JavaScript Timer clearInterval complications

So I'm attempting to make a Pomodoro Timer without using an API (I know, stupid choice) but I feel as if I'm over-complicating this issue.
I forked my CodePen so I could post the current code here without confusing anyone. My Code Pen
To see my issue: Just set Timer to .1 and Break to .1 - You'll see the Start to Resume works fine, but the Resume to start has issues.
I built in consoleLogs to track it and I see the Work Timer TRIES to start but then breakTimer over-runs it, and duplicates on every pass.
Why isn't my clearInterval working?
Things I've tried:
Adjusting names of clearInterval,
Setting it so it goes back to startTimer instead of start
force quitting it (instead of looping it back to startInterval.
The function is virtually identical to my startFunction yet fails to work properly. Would appreciate any input (I'm new to clearInterval but I believe I am using it right.)
function breakTimer() {
$('.jumbotron').css('visibility', 'visible');
setInterval(function() {
console.log("Break Timer...");
breakTime--;
if (breakTime < 0) {
clearInterval(timer);
working = false;
start();
} else {
showTime(breakTime);
}
}, 1000);
}
Edit:
To answer the reply:
function start() {
if (working == true){ //This keeps it from being spammable
return;
} //Else
workTime = $('#work').val()*60;
breakTime = $('#break').val()*60;
working = true;
checkStatus();
timer = startTimer();
}
Unsure if I should post every Function here
As per definition, the value returned by setInterval(...) is the ID of the created timer. As such, with your code you can only stop the last created timer because the ID in the timer variable gets overwritten, causing it to lose control over the previously created (and still running) timers.
The ID is what you pass on to clearInterval(...) to stop a timer. You will have to do this in a different way. You may ask for a different way in https://codereview.stackexchange.com/

How many timers in a window? [duplicate]

I have to use atleast 2 setTimeouts and 1 setInterval. Does this have any dependency on the browser or javascript engine being used?
tl;dr: Don't worry about the cost of timers until you're creating 100K's of them.
I just did a quick test of timer performance by creating this test file (creates 100K timers over and over):
<script>
var n = 0; // Counter used to verify all timers fire
function makeTimers() {
var start = Date.now();
for (var i = 0; i < 100000; i++, n++) {
setTimeout(hello, 5000);
}
console.log('Timers made in', Date.now() - start, 'msecs');
}
function hello() {
if (--n == 0) {
console.log('All timers fired');
makeTimers(); // Do it again!
}
}
setTimeout(makeTimers, 10000); // Wait a bit before starting test
</script>
I opened this file in Google Chrome (v54) on my circa ~2014 Macbook Pro, and went to the Timeline tab in Developer Tools and recorded the memory profile as the page loaded and ran thru 3-4 cycles of the test.
Observations
The timer creation loop takes 200ms. The page heap size starts at 3.5MB pre-test, and levels out at 3.9MB.
Conclusion
Each timer takes ~.002 msecs to set up, and adds about 35 bytes to the JS heap.
On a page you can have as many setTimeouts/setIntervals running at once as you wish, however in order to control each individually you will need to assign them to a variable.
var interval_1 = setInterval("callFunc1();",2000);
var interval_2 = setInterval("callFunc2();",1000);
clearInterval(interval_1);
The same code above applies to setTimeout, simply replacing the wording.
As Kevin has stated, JavaScript is indeed single threaded, so while you can have multiple timers ticking at once, only one can fire at any one time - i.e. if you have one that fires a function which 'halts' in execution, for example with an alert box, then that JS must be 'resumed' before another can trigger I believe.
One further example is given below. While the markup is not valid, it shows how timeouts work.
<html>
<body>
<script type="text/javascript">
function addThing(){
var newEle = document.createElement("div");
newEle.innerHTML = "Timer1 Tick";
document.body.appendChild(newEle);
}
var t1= setInterval("addThing();",1000);
var t2 = setInterval("alert('moo');",2000);
</script>
</body>
</html>
You can use as many as you want. Just remember that JavaScript is single threaded, so none of them can execute in parallel.
var interval_1 = setInterval("callFunc1();",2000); calls eval() which is evil so it's BAD.
Use this instead var interval_1 = setInterval(callFunc1,2000);
And for the question, you may use as many as you want but if all have the same interval between two actions, you better do it this way
var interval = setInterval(function() {
// function1
fct1();
// function2
fct2();
},2000);

Javascript Poll server. Will this cause a stack overflow?

I am not too familiar with the specifics of every javascript implementation on each browser. I do know however that using setTimeout, the method passed in gets called on a separate thread. So would using a setTimeout recursively inside of a method cause its stack to grow indefinitely until it causes a Stack Overflow? Or would it create a separate callstack and destroy the current frame once it goes out of focus? Here is the code that I'm wondering about.
function pollServer()
{
$.getJSON("poll.php", {}, function(data){
window.setTimeout(pollServer, 1000);
});
}
window.setTimeout(pollServer, 0);
I want to poll the server every second or so, but do not want to waste CPU cycles with a 'blocking loop' - also I do not want to set a timelimit on how long a user can access a page either before their browser dies.
EDIT
Using firebug, I set a few breakpoints and by viewing the "Script -> Stack" panel saw that the call stack is literally just "pollServer" and it doesn't grow per call. This is good - however, do any other implementations of JS act differently?
I am not sure if it would create a stack overflow, but I suggest you use setInterval if the period is constant.
This is how prototype implements its PeriodicalExecuter.
// Taken from Prototype (www.prototypejs.org)
var PeriodicalExecuter = Class.create({
initialize: function(callback, frequency) {
this.callback = callback;
this.frequency = frequency;
this.currentlyExecuting = false;
this.registerCallback();
},
registerCallback: function() {
this.timer = setInterval(this.onTimerEvent.bind(this), this.frequency * 1000);
},
execute: function() {
this.callback(this);
},
stop: function() {
if (!this.timer) return;
clearInterval(this.timer);
this.timer = null;
},
onTimerEvent: function() {
if (!this.currentlyExecuting) {
try {
this.currentlyExecuting = true;
this.execute();
} finally {
this.currentlyExecuting = false;
}
}
}
});
setTimeout executes sometime later in the future in the event pump loop. Functions passed to setTimeout are not continuations.
If you stop and think about it, what useful purpose or evidencec is there that the call stack is shared by the timeout function.
If they were shared what stack would be shared from the setter to the timeout function ?
Given the setter can do a few returns and pop some frames - what would be passed ?
Does the timeout function block the original thread ?
Does the statement after the setTimeout function execute after the timeout executes ?
Once you answer those questions it clearly becomes evident the answerr is NO.
setTimeout does not grow the callstack, because it returns immediately. As for whether your code will run indefinitely in any browser, I'm not sure, but it seems likely.
take a look at the jQuery "SmartUpdater" plugin.
http://plugins.jquery.com/project/smartupdater
Following features are available:
stop() - to stop updating.
restart() - to start updating after pause with resetting time interval to minTimeout.
continue() - to start updating after pause without resetting time interval.
status attribute - shows current status ( running | stopping | undefined )
updates only if new data is different from the old one.
multiplies time interval each time when data is not changed.
handle ajax failures by stopping to request data after "maxFailedRequests".

How can I run some code on all the nodes in a tree?

I want to run some code on all my treeView nodes depending on a value returned from the database and repeat this until a certain value is returned.
I was thinking that:
Give all my tree nodes the same css class so I can access them from JQuery
have a timer in my JQuery function that used ajax to go to the database, when a certain value is returned then stop the timer
Two questions here. How can I make my function run for each of the nodes and how do I do a timer in JavaScript, so:
$(function(){
$('cssClassOfAllMyNodes').WhatFunctionToCallHere?((){
//How do I do Timer functionality in JavaScript?
ForEachTimeInterval
{
//use Ajax to go to database and retrieve a value
AjaxCallBackFunction(result)
{
if (result = 1)
//How to stop the timer here?
}
}
});
});
Hope i'm clear. Thanks a lot
thanks a lot for the answer. And i would like you to comment on the design.
Bascially what i'm trying to acheive is a Windows Wokflow type functionality where each node in my tree updates its image depending on its status, where its status is got from querying the database with a key unique to the tree node. I'm open to ideas on other ways to implement this if you have any. thanks again
Without commenting on your design you can refer to these
$.each()
setTimeout() or setInterval()
You can do:
$(function(){
$('cssClassOfAllMyNodes').each(function (){
// Do something with "this" - "this" refers to current node.
});
});
Te proper way to handle timers in JS is to have a reference to each timeout or interval and then clearing them out.
The difference between them is:
The timeout will only run once, unless stopped before;
The interval will run indefinitely, until stopped.
So you can do something like:
var delay = 2000; // miliseconds
var timer = setTimeout("functionToBeCalled", delay);
clearTimeout(timer); // whenever you need.
Please note you can pass a string to setTimeout (same with setInterval) with the name of the function to be called. Or you could pass a reference to the function itself:
var callback = function () { alert(1); };
var timer = setTimeout(callback, delay);
Be sure not to set an Interval for AJAX requests, because you response might be delayed and successive calls to the server could eventually overlap.
Instead, you should call setTimeout and when the answer arrives then call setTimeout again.

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