This question already has answers here:
Controlling fps with requestAnimationFrame?
(15 answers)
Closed 3 years ago.
I'm trying to make a web-based game and I use setInterval to update the game (positions, collision checks, etc...) 60 times a second.
It works fine in most browsers, but for some reason Firefox sometimes throttles it to about 35 times a second. Yes, sometimes. If DevTools is closed, it will throttle, but if you open DevTools and start recording performance, it jumps to 60 and will stay that way until DevTools is closed.
If you're using Firefox, run the snippet and try it:
var cycles = 0;
setInterval(()=>{
cycles++;
}, 1000/60);
setInterval(()=>{
console.log("Update cycles per second: %i", cycles);
cycles = 0;
}, 1000);
Is this a bug? If not, why does this happen and how can I work around it?
Edit: I'm not using setInterval to render. For that I use requestAnimationFrame. I'm using setInterval to update the game at a constant time interval, because requestAnimationFrame fires before repainting, and is heavily dependent on the refresh rate of the user's screen.
You should not rely on timers being accurate. They often aren't. Instead, rely on time being accurate:
var cycles = 0, start = Date.now();
setInterval(() => {
cycles = Math.floor((Date.now() - start) / 1000 * 60);
}, 1000/60);
That said, requestAnimationFrame is probably a better choice for your use than setInterval, as it gets called on every rerender.
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
This question already has answers here:
How to create an accurate timer in javascript?
(15 answers)
Closed 6 years ago.
I need to generate an event exactly every 1s. I'm testing setTimeout function as following:
window.onload = function() {
var oldTime = Date.now();
setTimeout(function printTime() {
newTime = Date.now();
console.log(newTime - oldTime);
oldTime = newTime;
setTimeout(printTime, 1000);
}, 1000);
}
It returns 1s with a little bit offset:
testTimeout.js:6 1005
testTimeout.js:6 1006
2testTimeout.js:6 1001
testTimeout.js:6 1006
testTimeout.js:6 1005
testTimeout.js:6 1006
testTimeout.js:6 1005
Where does the offset come from? Is it because of the oldTime and newTime calculation?
I need to generate an event exactly every 1s.
There is no way to do this with exact precision.
The time passed to setTimeout is the minimum guaranteed time in which your code will run, not the exact time.
The time represents in how many milliseconds the JS Engine will push that function to the Event Queue. Once the function is in the Event Queue, it runs after all the current tasks present in the queue, such as events and other timers, which will create a delay.
Additionally, no task can be executed from the Event Queue while any regular JS code is running which could also potentially create small delays.
For example, this function test:
setTimeout(function test() {
console.log('second');
}, 0);
for (i = 0; i < 1000000; i++); // the number 1000000 is an arbitrary big number
console.log('first');
Will run after the loop below it has finished, which will be more than 0 milliseconds away.
In fact, if that loop was infinite, the setTimeout callback will never fire.
Note: As mentioned by nnnnnn in the comments, the actual minimum time, as per the HTML5 spec, in which setTimeout will push a function to the Event Queue is 4ms, regardless if we put less. Previously that limit used to be 10ms.
MDN
In fact, 4 ms 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.
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
Today I was introduced to the world of Web Workers in JavaScript. This made me rethink about timers. I used to program timers the ugly way, like this.
var time = -1;
function timerTick()
{
time++;
setTimeout("timerTick()",1000);
$("#timeI").html(time);
}
I know this could be improved by saving the date when you start the timer, but I've never been a fan of that.
Now I came up with a method using Web Workers, I did a little benchmark and found it much more reliable. Since I am not an expert on JavaScript I would like to know if this function works correct or what problems it might have thanks in advance.
My JavaScript code (please note I use JQuery):
$(function() {
//-- Timer using web worker.
var worker = new Worker('scripts/task.js'); //External script
worker.onmessage = function(event) { //Method called by external script
$("#timeR").html(event.data)
};
};
The external script ('scripts/task.js'):
var time = -1;
function timerTick()
{
time++;
setTimeout("timerTick()",1000);
postMessage(time);
}
timerTick();
You can also view a live demo on my website.
If you're trying to reliably display seconds ticking by, then the ONLY reliable way to do that is to get the current time at the start and use the timer ONLY for updating the screen. On each tick, you get the current time, compute the actual elapsed seconds and display that. Neither setTimeout() nor setInterval() are guaranteed or can be used for accurately counting time.
You can do it like this:
var start = +(new Date);
setInterval(function() {
var now = +(new Date);
document.getElementById("time").innerHTML = Math.round((now - start)/1000);
}, 1000);
If the browser gets busy and timers are erratically spaced, you may get a slightly irregular update on screen, but the elapsed time will remain accurate when the screen is updated. Your method is susceptible to accumulating error in the elapsed time.
You can see this work here: http://jsfiddle.net/jfriend00/Gfwze/
The most accurate timer would be a comparison of two time stamps. You could increase the precision of your timer by updating more frequently (such as every 100ms). I prefer using setInterval() over setTimeout().