Something that has always bugged me is how unpredictable the setTimeout() method in Javascript is.
In my experience, the timer is horribly inaccurate in a lot of situations. By inaccurate, I mean the actual delay time seems to vary by 250-500ms more or less. Although this isn't a huge amount of time, when using it to hide/show UI elements the time can be visibly noticeable.
Are there any tricks that can be done to ensure that setTimeout() performs accurately (without resorting to an external API) or is this a lost cause?
Are there any tricks that can be done
to ensure that setTimeout() performs
accurately (without resorting to an
external API) or is this a lost cause?
No and no. You're not going to get anything close to a perfectly accurate timer with setTimeout() - browsers aren't set up for that. However, you don't need to rely on it for timing things either. Most animation libraries figured this out years ago: you set up a callback with setTimeout(), but determine what needs to be done based on the value of (new Date()).milliseconds (or equivalent). This allows you to take advantage of more reliable timer support in newer browsers, while still behaving appropriately on older browsers.
It also allows you to avoid using too many timers! This is important: each timer is a callback. Each callback executes JS code. While JS code is executing, browser events - including other callbacks - are delayed or dropped. When the callback finishes, additional callbacks must compete with other browser events for a chance to execute. Therefore, one timer that handles all pending tasks for that interval will perform better than two timers with coinciding intervals, and (for short timeouts) better than two timers with overlapping timeouts!
Summary: stop using setTimeout() to implement "one timer / one task" designs, and use the real-time clock to smooth out UI actions.
.
REF; http://www.sitepoint.com/creating-accurate-timers-in-javascript/
This site bailed me out on a major scale.
You can use the system clock to compensate for timer inaccuracy. If you run a timing function as a series of setTimeout calls — each instance calling the next — then all you have to do to keep it accurate is work out exactly how inaccurate it is, and subtract that difference from the next iteration:
var start = new Date().getTime(),
time = 0,
elapsed = '0.0';
function instance()
{
time += 100;
elapsed = Math.floor(time / 100) / 10;
if(Math.round(elapsed) == elapsed) { elapsed += '.0'; }
document.title = elapsed;
var diff = (new Date().getTime() - start) - time;
window.setTimeout(instance, (100 - diff));
}
window.setTimeout(instance, 100);
This method will minimize drift and reduce the inaccuracies by more than 90%.
It fixed my issues, hope it helps
I had a similar problem not long ago and came up with an approach which combines requestAnimationFrame with performance.now() which works very effectively.
Im now able to make timers accurate to approx 12 decimal places:
window.performance = window.performance || {};
performance.now = (function() {
return performance.now ||
performance.mozNow ||
performance.msNow ||
performance.oNow ||
performance.webkitNow ||
function() {
//Doh! Crap browser!
return new Date().getTime();
};
})();
http://jsfiddle.net/CGWGreen/9pg9L/
If you need to get an accurate callback on a given interval, this gist may help you:
https://gist.github.com/1185904
function interval(duration, fn){
var _this = this
this.baseline = undefined
this.run = function(){
if(_this.baseline === undefined){
_this.baseline = new Date().getTime()
}
fn()
var end = new Date().getTime()
_this.baseline += duration
var nextTick = duration - (end - _this.baseline)
if(nextTick<0){
nextTick = 0
}
_this.timer = setTimeout(function(){
_this.run(end)
}, nextTick)
}
this.stop = function(){
clearTimeout(_this.timer)
}
}
shog9's answer is pretty much what I'd say, although I'd add the following about UI animation/events:
If you've got a box that's supposed to slide onto the screen, expand downwards, then fade in its contents, don't try to make all three events separate with delays timed to make them fire one after another - use callbacks, so once the first event is done sliding it calls the expander, once that's done it calls the fader. jQuery can do it easily, and I'm sure other libraries can as well.
If you're using setTimeout() to yield quickly to the browser so it's UI thread can catch up with any tasks it needs to do (such as updating a tab, or to not show the Long Running Script dialog), there is a new API called Efficient Script Yielding, aka, setImmediate() that may work a bit better for you.
setImmediate() operates very similarly to setTimeout(), yet it may run immediately if the browser has nothing else to do. In many situations where you are using setTimeout(..., 16) or setTimeout(..., 4) or setTimeout(..., 0) (i.e. you want the browser to run any outstanding UI thread tasks and not show a Long Running Script dialog), you can simply replace your setTimeout() with setImmediate(), dropping the second (millisecond) argument.
The difference with setImmediate() is that it is basically a yield; if the browser has sometime to do on the UI thread (e.g., update a tab), it will do so before returning to your callback. However, if the browser is already all caught up with its work, the callback specified in setImmediate() will essentially run without delay.
Unfortunately it is only currently supported in IE9+, as there is some push back from the other browser vendors.
There is a good polyfill available though, if you want to use it and hope the other browsers implement it at some point.
If you are using setTimeout() for animation, requestAnimationFrame is your best bet as your code will run in-sync with the monitor's refresh rate.
If you are using setTimeout() on a slower cadence, e.g. once every 300 milliseconds, you could use a solution similar to what user1213320 suggests, where you monitor how long it was from the last timestamp your timer ran and compensate for any delay. One improvement is that you could use the new High Resolution Time interface (aka window.performance.now()) instead of Date.now() to get greater-than-millisecond resolution for the current time.
You need to "creep up" on the target time. Some trial and error will be necessary but in essence.
Set a timeout to complete arround 100ms before the required time
make the timeout handler function like this:
calculate_remaining_time
if remaining_time > 20ms // maybe as much as 50
re-queue the handler for 10ms time
else
{
while( remaining_time > 0 ) calculate_remaining_time;
do_your_thing();
re-queue the handler for 100ms before the next required time
}
But your while loop can still get interrupted by other processes so it's still not perfect.
Here's an example demoing Shog9's suggestion. This fills a jquery progress bar smoothly over 6 seconds, then redirects to a different page once it's filled:
var TOTAL_SEC = 6;
var FRAMES_PER_SEC = 60;
var percent = 0;
var startTime = new Date().getTime();
setTimeout(updateProgress, 1000 / FRAMES_PER_SEC);
function updateProgress() {
var currentTime = new Date().getTime();
// 1000 to convert to milliseconds, and 100 to convert to percentage
percent = (currentTime - startTime) / (TOTAL_SEC * 1000) * 100;
$("#progressbar").progressbar({ value: percent });
if (percent >= 100) {
window.location = "newLocation.html";
} else {
setTimeout(updateProgress, 1000 / FRAMES_PER_SEC);
}
}
This is a timer I made for a music project of mine which does this thing. Timer that is accurate on all devices.
var Timer = function(){
var framebuffer = 0,
var msSinceInitialized = 0,
var timer = this;
var timeAtLastInterval = new Date().getTime();
setInterval(function(){
var frametime = new Date().getTime();
var timeElapsed = frametime - timeAtLastInterval;
msSinceInitialized += timeElapsed;
timeAtLastInterval = frametime;
},1);
this.setInterval = function(callback,timeout,arguments) {
var timeStarted = msSinceInitialized;
var interval = setInterval(function(){
var totaltimepassed = msSinceInitialized - timeStarted;
if (totaltimepassed >= timeout) {
callback(arguments);
timeStarted = msSinceInitialized;
}
},1);
return interval;
}
}
var timer = new Timer();
timer.setInterval(function(){console.log("This timer will not drift."),1000}
Hate to say it, but I don't think there is a way to alleviate this. I do think that it depends on the client system, though, so a faster javascript engine or machine may make it slightly more accurate.
To my experience it is lost effort, even as the smallest reasonable amount of time I ever recognized js act in is around 32-33 ms. ...
There is definitely a limitation here. To give you some perspective, the Chrome browser Google just released is fast enough that it can execute setTimeout(function() {}, 0) in 15-20 ms whereas older Javascript engines took hundreds of milliseconds to execute that function. Although setTimeout uses milliseconds, no javascript virtual machine at this point in time can execute code with that precision.
Dan, from my experience (that includes implementation of SMIL2.1 language in JavaScript, where time management is in subject) I can assure you that you actually never need high precision of setTimeout or setInterval.
What does however matter is the order in which setTimeout/setInterval gets executed when queued - and that always works perfectly.
JavaScript timeouts have a defacto limit of 10-15ms (I'm not sure what you're doing to get 200ms, unless you're doing 185ms of actual js execution). This is due to windows having a standard timer resolution of 15ms, the only way to do better is to use Windows' higher resolution timers which is a system wide setting so can screw with other applications on the system and also chews battery life (Chrome has a bug from Intel on this issue).
The defacto standard of 10-15ms is due to people using 0ms timeouts on websites but then coding in a way that assumes that assumes a 10-15ms timeout (eg. js games which assume 60fps but ask 0ms/frame with no delta logic so the game/site/animation goes a few orders of magnitude faster than intended). To account for that, even on platforms that don't have windows' timer problems, the browsers limit timer resolution to 10ms.
Here are what I use. Since it's JavaScript, I will post both my Frontend and node.js solutions:
For both, I use the same decimal rounding function that I highly recommend you keep at arms length because reasons:
const round = (places, number) => +(Math.round(number + `e+${places}`) + `e-${places}`)
places - Number of decimal places at which to round, this should be safe and should avoid any issues with floats (some numbers like 1.0000000000005~ can be problematic). I Spent time researching the best way to round decimals provided by high-resolution timers converted to milliseconds.
that + symbol - It is a unary operator that converts an operand into a number, virtually identical to Number()
Browser
const start = performance.now()
// I wonder how long this comment takes to parse
const end = performance.now()
const result = (end - start) + ' ms'
const adjusted = round(2, result) // see above rounding function
node.js
// Start timer
const startTimer = () => process.hrtime()
// End timer
const endTimer = (time) => {
const diff = process.hrtime(time)
const NS_PER_SEC = 1e9
const result = (diff[0] * NS_PER_SEC + diff[1])
const elapsed = Math.round((result * 0.0000010))
return elapsed
}
// This end timer converts the number from nanoseconds into milliseconds;
// you can find the nanosecond version if you need some seriously high-resolution timers.
const start = startTimer()
// I wonder how long this comment takes to parse
const end = endTimer(start)
console.log(end + ' ms')
You could consider using the html5 webaudio clock which uses the system time for better accuracy
I want to make a JavaScript animation take 5 seconds to complete using requestAnimationFrame().
I don't want a strict and precise timing, so anything close to 5 seconds is OK and I want my code to be simple and readable, so solutions like this won't work for me.
My question is, is it safe to assume most browsers render the page at 60 fps? i.e. if I want my animation to take 5 seconds to complete, I'll divide it to 60 * 5 = 300 steps and with each call of function draw() using requestAnimationFrame(), draw the next step of animation. (Given the fact the animation is pretty simple, just moving a colored div around.)
By the way, I can't use jQuery.
Edit: Let me rephrase the question this way: Do all browsers 'normally' try to render the page at 60 fps? I want to know if Chrome for example renders at 75 fps or Firefox renders at 70 fps.
(Normal condition: CPU isn't highly loaded, RAM is not full, there are no storage failures, room is properly ventilated and nobody tries to throw my laptop out the window.)
Relying on 60 frames per second is very unsafe, because the browser isn't always in the same conditions, and even if it tries to render the page at the maximum fps possible, there's always a chance of the processor/cpu/gpu being busy doing something else, causing the FPS to drop down.
If you want to rely on FPS (although I wouldn't suggest you so), you should first detect the current fps, and adjust the speed of your animation frame per frame. Here's an example:
var lastCall, fps;
function detectFps() {
var delta;
if (lastCall) {
delta = (Date.now() - lastCall)/1000;
lastCall = Date.now();
fps = 1/delta;
} else {
lastCall = Date.now();
fps = 0;
}
}
function myFunc() {
detectFps();
// Calculate the speed using the var fps
// Animate...
requestAnimationFrame(myFunc);
}
detectFps(); // Initialize fps
requestAnimationFrame(myFunc); // Start your animation
It depends on the GPU and monitor combination. I have a good GPU and a 120 hertz monitor, so it renders at 120 fps. During the render, If I move to 60 hertz monitor, it will max out at 60 fps.
Another factor, that happens in some browsers/OS, is the iGPU being used instead of the discrete gpu.
As already stated by others, it isn't.
But if you need to end your animation in approximately 5 seconds and it's not crucial not to miss any frames in the animation, you can use the old setTimeout() way. That way you can miss a target by a few milliseconds, and some of the frames in your animation will be skipped (not rendered) because of the fps mismatch, but this can be a "good enough" solution, especially if your animation is simple as you state it is, there's a chance that users won't even see the glitch.
It's not safe to assume everyone can handle animation.
People will have different needs.
A lot of common animations, and common web design practices, give me awful migraines, so I set my browser to 1 frame per second to kill the animation without causing too much fast flashing.
As I was looking for a simple Stopwatch implementation in JS, I found this code http://codepen.io/_Billy_Brown/pen/dbJeh/
The problem is that it's not working fine, the clock go way too fast. I got 30 seconds on the screen when i got only 23 seconds on my watch.
And I don't understand why. The timer function is called every millisecond and should be updating the time correctly.
setInterval(this.timer, 1);
Is the problem coming from the browser or from the JS code.
Thanks in advance.
The timers in Javascript doesn't have millisecond precision.
There is a minimum time for the interval, which differs depending on the browser and browser version. Typical minimums are 4 ms for recent browsers and 10 ms for a little older browsers.
Also, you can't rely on the callback being called at exact the time that you specify. Javascript is single threaded, which means that if some other code is running when the timer triggers a tick, it has to wait until that other code finishes.
In fact the code you gave is imitating time flow, but it is not synchronized with system time.
Every millisecond it just invokes the function this.time, which performs recounting of millis, seconds and so on
without getting native system time, but just adding 1 to variable representing "imaginary milliseconds".
So we can say that resulting pseudo-time you see depends on your CPU, browser and who knows what else.
On our modern fantastically fast computers the body of this.time function is being executed faster than millisecond (wondering what would happen on Pentium 2 with IE5 on board).
Anyhow there is no chance for the this.time to be executed exactly in particular fixed period on all computers and browsers.
The simplest correct way to show the time passed since startpoint according to the system time is:
<body>
<script>
var startTime = new Date() // assume this initialization to be start point
function getTimeSinceStart()
{
var millisSinceStart = new Date() - startTime
, millis = millisSinceStart % 1000
, seconds = Math.floor(millisSinceStart / 1000)
return [seconds, millis].join( ':' )
}
(function loop()
{
document.title = getTimeSinceStart() // look on the top of page
setTimeout( loop, 10 )
}())
</script>
</body>
P.S. What #Guffa says in his answer is correct (generally for js in browsers), but in this case it does not matter and not affect the problem
This question already has an answer here:
Are there any standards for mobile device web browsers in terms of thread sleeping? [closed]
(1 answer)
Closed 8 years ago.
I'm developing a chronometer app in Tizen and I'm currently using the setInterval function to schedule the next time the text with the numbers will be updated:
chrono : function() {
SecondsChrono += 1;
},
setInterval(chrono(), 1000);
But when the device's screen is put on "sleep mode" the chronometer gets delayed.
I want to know if anyone has experienced this and if you have some way to avoid it or if you have any advice for me to implement this chronometer in another way.
You should use setInterval only to update the screen, to see how much time has ellapsed since the chronometer first started you should do something like this:
var SCREEN_UPDATE_REFRESH_RATE= 1000;
var startTime= (new Date()).getTime();
var updateScreen= function() {
var currentTime= (new Date()).getTime();
var timeEllapsed = currentTime - startTime; //this value is in milliseconds
document.write("Ellapesed time in seconds: " timeEllapsed / 1000);
setTimeout(updateScreen, SCREEN_UPDATE_REFRESH_RATE);
}
updateScreen();
It is better to use setTimeout in this case than setInterval. The difference between the two is that setInterval schedules the function to execute forever every X milliseconds while setTimeout schedules to execute once and then never again, in this case the function sets a new timeout that keeps the updating process forever. If your user system is overloaded various setInterval callbacks can be chained together which can freeze the user browser. See this for more information.
I have a method changeColor that updates the CSS on some elements in my HTML.
I also have a timer that controls this being applied i.e:
var timer = setInterval(changeColor,0);
The problem i'm facing is using that time interval of 0 results in the changeColor method not being run, however if i change it something minimal like:
var timer = setInterval(changeCalendarColor,1);
it works.
Now i'd be happy to use this however in IE8 this causes a slight delay in the colors appearing.
Any ideas on how to resolve this?
Thanks.
The setInterval function takes a function to call and a delay in milliseconds. You cannot have a delay of 0 milliseconds; there is a minimum delay in place (which according to the specs is 4ms). Take a look at the documentation for more.
// To call a function every second:
var timer = setInterval(myFunction, 1000);
// This doesn't throw an error as the 0 is being overridden by a default minimum:
var timer = setInterval(myFunction, 0);
If you want to call the function initially and ALSO every second after that, you should call the function when you set the interval:
var timer = setInterval(myFunction, 1000);
myFunction();
Here's what the Mozilla docs say about the minimum delay:
"In fact, 4ms is specified by the HTML5 spec and is consistent across browsers released in 2010 and onward. Prior to (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), the minimum timeout value for nested timeouts was 10 ms."
Regarding the slowness on IE8, the setInterval "lag" is probably being caused by IE8 being too slow to keep up with what the function is trying to do. At each time interval, the function is called, but IE8 is queue is being overloaded as a result -- to the point that IE8 can't keep up. Increasing the delay would mask this issue I'd imagine.
As Vasile says on this Google Code forum:
"When a new call is triggered if the previous call is not ended then the new call is queued and will wait for it's time to be executed; and here is the problem... (the timer will slow down when the queue will grow and the performance will go down over time)"
Note that this is a common problem for low delays in IE8; check this post for more on this specific issue.
Also, a quick point to note about setInterval delays is that inactive tabs are occasionally treated differently:
"In (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2) and Chrome 11, timeouts are clamped to firing no more often than once per second (1000ms) in inactive tabs..."
See this related SO post for more.