Are there any timing functions in JavaScript with microsecond resolution?
I am aware of timer.js for Chrome, and am hoping there will be a solution for other friendly browsers, like Firefox, Safari, Opera, Epiphany, Konqueror, etc. I'm not interested in supporting any IE, but answers including IE are welcome.
(Given the poor accuracy of millisecond timing in JS, I'm not holding my breath on this one!)
Update: timer.js advertises microsecond resolution, but it simply multiplies the millisecond reading by 1,000. Verified by testing and code inspection. Disappointed. :[
As alluded to in Mark Rejhon's answer, there is an API available in modern browsers that exposes sub-millisecond resolution timing data to script: the W3C High Resolution Timer, aka window.performance.now().
now() is better than the traditional Date.getTime() in two important ways:
now() is a double with submillisecond resolution that represents the number of milliseconds since the start of the page's navigation. It returns the number of microseconds in the fractional (e.g. a value of 1000.123 is 1 second and 123 microseconds).
now() is monotonically increasing. This is important as Date.getTime() can possibly jump forward or even backward on subsequent calls. Notably, if the OS's system time is updated (e.g. atomic clock synchronization), Date.getTime() is also updated. now() is guaranteed to always be monotonically increasing, so it is not affected by the OS's system time -- it will always be wall-clock time (assuming your wall clock is not atomic...).
now() can be used in almost every place that new Date.getTime(), + new Date and Date.now() are. The exception is that Date and now() times don't mix, as Date is based on unix-epoch (the number of milliseconds since 1970), while now() is the number of milliseconds since your page navigation started (so it will be much smaller than Date).
now() is supported in Chrome stable, Firefox 15+, and IE10. There are also several polyfills available.
Note: When using Web Workers, the window variable isn't available, but you can still use performance.now().
There's now a new method of measuring microseconds in javascript:
http://gent.ilcore.com/2012/06/better-timer-for-javascript.html
However, in the past, I found a crude method of getting 0.1 millisecond precision in JavaScript out of a millisecond timer. Impossible? Nope. Keep reading:
I'm doing some high-precisio experiments that requires self-checked timer accuracies, and found I was able to reliably get 0.1 millisecond precision with certain browsers on certain systems.
I have found that in modern GPU-accelerated web browsers on fast systems (e.g. i7 quad core, where several cores are idle, only browser window) -- I can now trust the timers to be millisecond-accurate. In fact, it's become so accurate on an idle i7 system, I've been able to reliably get the exact same millisecond, over more than 1,000 attempts. Only when I'm trying to do things like load an extra web page, or other, the millisecond accuracy degrades (And I'm able to successfully catch my own degraded accuracy by doing a before-and-after time check, to see if my processing time suddenly lengthened to 1 or more milliseconds -- this helps me invalidate results that has probably been too adversely affected by CPU fluctuations).
It's become so accurate in some GPU accelerated browsers on i7 quad-core systems (when the browser window is the only window), that I've found I wished I could access a 0.1ms precision timer in JavaScript, since the accuracy is finally now there on some high-end browsing systems to make such timer precision worthwhile for certain types of niche applications that requires high-precision, and where the applications are able to self-verify for accuracy deviations.
Obviously if you are doing several passes, you can simply run multiple passes (e.g. 10 passes) then divide by 10 to get 0.1 millisecond precision. That is a common method of getting better precision -- do multiple passes and divide the total time by number of passes.
HOWEVER...If I can only do a single benchmark pass of a specific test due to an unusually unique situation, I found out that I can get 0.1 (And sometimes 0.01ms) precision by doing this:
Initialization/Calibration:
Run a busy loop to wait until timer increments to the next millisecond (align timer to beginning of next millisecond interval) This busy loop lasts less than a millisecond.
Run another busy loop to increment a counter while waiting for timer to increment. The counter tells you how many counter increments occured in one millisecond. This busy loop lasts one full millisecond.
Repeat the above, until the numbers become ultra-stable (loading time, JIT compiler, etc). 4. NOTE: The stability of the number gives you your attainable precision on an idle system. You can calculate the variance, if you need to self-check the precision. The variances are bigger on some browsers, and smaller on other browsers. Bigger on faster systems and slower on slower systems. Consistency varies too. You can tell which browsers are more consistent/accurate than others. Slower systems and busy systems will lead to bigger variances between initialization passes. This can give you an opportunity to display a warning message if the browser is not giving you enough precision to allow 0.1ms or 0.01ms measurements. Timer skew can be a problem, but some integer millisecond timers on some systems increment quite accurately (quite right on the dot), which will result in very consistent calibration values that you can trust.
Save the final counter value (or average of the last few calibration passes)
Benchmarking one pass to sub-millisecond precision:
Run a busy loop to wait until timer increments to the next millisecond (align timer to beginning of next millisecond interval). This busy loop lasts less than a millisecond.
Execute the task you want to precisely benchmark the time.
Check the timer. This gives you the integer milliseconds.
Run a final busy loop to increment a counter while waiting for timer to increment. This busy loop lasts less than a millisecond.
Divide this counter value, by the original counter value from initialization.
Now you got the decimal part of milliseconds!!!!!!!!
WARNING: Busy loops are NOT recommended in web browsers, but fortunately, these busy loops run for less than 1 millisecond each, and are only run a very few times.
Variables such as JIT compilation and CPU fluctuations add massive inaccuracies, but if you run several initialization passes, you'll have full dynamic recompilation, and eventually the counter settles to something very accurate. Make sure that all busy loops is exactly the same function for all cases, so that differences in busy loops do not lead to differences. Make sure all lines of code are executed several times before you begin to trust the results, to allow JIT compilers to have already stabilized to a full dynamic recompilation (dynarec).
In fact, I witnessed precision approaching microseconds on certain systems, but I wouldn't trust it yet. But the 0.1 millisecond precision appears to work quite reliably, on an idle quad-core system where I'm the only browser page. I came to a scientific test case where I could only do one-off passes (due to unique variables occuring), and needed to precisely time each pass, rather than averaging multiple repeat pass, so that's why I did this.
I did several pre-passes and dummy passes (also to settle the dynarec), to verify reliability of 0.1ms precision (stayed solid for several seconds), then kept my hands off the keyboard/mouse, while the benchmark occured, then did several post-passes to verify reliability of 0.1ms precision (stayed solid again). This also verifies that things such as power state changes, or other stuff, didn't occur between the before-and-after, interfering with results. Repeat the pre-test and post-test between every single benchmark pass. Upon this, I was quite virtually certain the results in between were accurate. There is no guarantee, of course, but it goes to show that accurate <0.1ms precision is possible in some cases in a web browser.
This method is only useful in very, very niche cases. Even so, it literally won't be 100% infinitely guaranteeable, you can gain quite very trustworthy accuracy, and even scientific accuracy when combined with several layers of internal and external verifications.
Here is an example showing my high-resolution timer for node.js:
function startTimer() {
const time = process.hrtime();
return time;
}
function endTimer(time) {
function roundTo(decimalPlaces, numberToRound) {
return +(Math.round(numberToRound + `e+${decimalPlaces}`) + `e-${decimalPlaces}`);
}
const diff = process.hrtime(time);
const NS_PER_SEC = 1e9;
const result = (diff[0] * NS_PER_SEC + diff[1]); // Result in Nanoseconds
const elapsed = result * 0.0000010;
return roundTo(6, elapsed); // Result in milliseconds
}
Usage:
const start = startTimer();
console.log('test');
console.log(`Time since start: ${endTimer(start)} ms`);
Normally, you might be able to use:
console.time('Time since start');
console.log('test');
console.timeEnd('Time since start');
If you are timing sections of code that involve looping, you cannot gain access to the value of console.timeEnd() in order to add your timer results together. You can, but it get gets nasty because you have to inject the value of your iterating variable, such as i, and set a condition to detect if the loop is done.
Here is an example because it can be useful:
const num = 10;
console.time(`Time til ${num}`);
for (let i = 0; i < num; i++) {
console.log('test');
if ((i+1) === num) { console.timeEnd(`Time til ${num}`); }
console.log('...additional steps');
}
Cite: https://nodejs.org/api/process.html#process_process_hrtime_time
The answer is "no", in general. If you're using JavaScript in some server-side environment (that is, not in a browser), then all bets are off and you can try to do anything you want.
edit — this answer is old; the standards have progressed and newer facilities are available as solutions to the problem of accurate time. Even so, it should be remembered that outside the domain of a true real-time operating system, ordinary non-privileged code has limited control over its access to compute resources. Measuring performance is not the same (necessarily) as predicting performance.
editing again — For a while we had performance.now(), but at present (2022 now) browsers have degraded the accuracy of that API for security reasons.
I have a function that does simple performance benchmarking of arbitrary JS function invocation like this:
function benchmark(f) {
var startTime = Date.now();
f();
var endTime = Date.now();
console.log('Elapsed: %d ms', endTime - startTime);
}
The functions that I test with it take typically 2-5s to execute, so the overhead of counting one full call to Date.now() is negligible.
Nevertheless, the benchmark times vary quite considerably based on what other processes happen to be running on my machine, so even if I run the benchmark several times and take the smallest value I can still see variations of 20-50% between between successive (sets of) runs—even when the machine is "mostly" idle. This makes it difficult to see performance changes of <5%.
I end up having to watch Activity Monitor and wait until the system looks (mostly) idle, then hope that nothing else starts up in the middle of the run. I'd like, instead, to modify the benchmark to measure elapsed CPU time instead of elapsed wall time. This should make it mostly insensitive to being blocked on I/O and considerably less sensitive to CPU contention (though not insensitive: due to hyper-threading I expect that if the number of runnable threads exceeds the number of physical CPU cores that the apparent performance will decrease as hyper-threads contend for actual hardware).
How can I query the elapsed CPU time of the node process from within Node?
I would hope that the faster my processor is, the faster my code would run.
I can measure code to the millisecond precision using.
new Date.getTime()
What is the correlation between the two?
How can I expect this to relate to say a processor running at 3.2 GHz.
Can anyone quantify this relationship even if it is a very rough estimate?
// start_time
run some simple code to be timed.
// end_time
The [EDIT: CPU]clock time that gets allotted to a JS script is determined by a number of factors, including:
browser/version
OS
current power state
A demonstration of this can be seen in Windows 8's Advanced Power Options menu. Expand the Internet Explorer node and you'll notice that the entry below is for JavaScript timer frequency. That's exactly what you think it is -- a setting which controls how often the JS clock 'ticks'. The more ticks in a second, the more often the JS engine gets to execute code, the more code executed, the more power it takes.
So to answer your question:
Yes, in the very general sense processor clock speed can determine how fast a particular JS runs, but it would be a mistake to assume that it is a straight-forward correlation.
EDIT (more info):
I can't dig a link but I'll update here if I find it. Using setTimeout or setInterval, the smallest unit of time you can pass into those methods that will actually be honored is 100(ms). It's possible to have higher frequencies than that, but 100ms is all that is guaranteed
I found something close to what I was thinking in this article:
http://javascript.info/tutorial/settimeout-setinterval
Essentially, in JavaScript timers operated on a queued basis -- you can call setTimeout(fn, 10), and your request will be queued to execute after 10ms, but that doesn't mean that it will get executed after that amount of time, just that it's queued to do so. If you measure the difference between expected and actual (above a threshold, probably 100ms) you could gather offset data to calculate the resulting frequency (or 'clock speed') the script is running at. See this article for an example of benchmarking JS in more precise ways
From that second article, we see that the minimum timeout you can get is 4ms:
Using setTimeout for measuring graphics performance is another bad idea. The setTimeout interval is capped to 4 ms in browsers, so the most you can get out of it is 250 FPS. Historically, browsers had different minimum intervals, so you might have had a very broken trivial draw benchmark that showed browser A running at 250 FPS (4 ms min interval) and browser B running at 100 FPS (10 ms min interval). Clearly A is faster! Not! It could well be that B ran the draw code faster than A, say A took 3 ms and B took 1 ms. Doesn’t affect the FPS, as the draw time is less than the minimum setTimeout interval. And if the browser renders asynchronously, all bets are off. Don’t use setTimeout unless you know what you’re doing.
I have to develop an application that will be required to measure user response time within a series of experiments. This application will be run on approximately 100 computers, thus I had mentioned that a browser based approach might be best to cut down on performing installs and updates. With that said, now that I've read about the accuracy of timers in browsers, specifically javascript timers, I'm learning there can be a delay from a few milliseconds to upwards of 10-15ms. This sort of delay would have a negative impact on the precision of these experiments when users measure their response time to visual queues on the screen.
Is there a known way around this to get precise timers for a web application being run within a browser through javascript? Likewise, some of these experiments require simple 2d animation, such as seeing how long a user can keep their mouse cursor over a rotating cube. I would prefer to use HTML5 and Javascript and we cannot use flash.
True you can't rely on a timer's interval, but you can rely on a new Date object. For instance:
var previousTime = new Date().getTime(); // returns milliseconds of "now"
var timer = setInterval( function() {
var currentTime = new Date().getTime();
var millisecondsSinceLastUpdate = currentTime - previousTime;
previousTime = currentTime;
alert( 'milliseconds since last update: ' + millisecondsSinceLastUpdate );
}, 1 );
Just as #dqhendricks suggests, you should use a new Date object. However, if you need this to be consistent and accurate you'd need this be run on the same computer with the same browser version and nothing running in the background.
Check out this demo in firefox and chrome. Click on the edge and move your cursor out as fast as you can - the lowest I can get in FF is 6MS, the lowest I can get in Chrome is 42MS.
These values can vary even wider between machines. I set up a VM with 512MB of RAM and 50% single core cap, opened up 5 tabs in FF and attempted the test - the lowest I've gotten is 52MS.
So unless you can control the users browser, PC and things running in the background I would not count on the data being accurate.
If you have new browsers you can use performance.now() which offers more precision than the Date object, but the other performance concerns of using the browser still apply :(
http://updates.html5rocks.com/2012/08/When-milliseconds-are-not-enough-performance-now
I am building a simple accelerometer app in PhoneGap primarily targeted to Android, and depending on what I set the frequency to, I get very inconsistent readings. If I set the frequency to 100, I get 10 measurements a second. However if I try something like frequency of 50ms or 40 or 10, I get very inconsistent readings of anything from 18 to 27 readings a second.
I think it comes down to the fact that setInterval is not guaranteed to fire at the interval that you provide. Since JavaScript is single threaded it may be busy doing something else when the interval time is reached. This would account for the variable readings you are getting.