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JavaScript Performance using console.time() & console.timeEnd()

Sanket Patel on September 08, 2018

Many a times it's necessary to check the time your code is taking to execute. JavaScript runs on the client's local machine and we don't want our a...

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Adrian B.G. • Sep 9 '18

I think that this is the definition of "hacky", you change the code you are trying to measure. Is like using console.log instead of breakpoints.

We used this method 5-10yrs ago when we do not have the required tools, but now you do not need them, you have dev tools developers.google.com/web/tools/ch...

Sanket Patel • Sep 10 '18

Yes @bgadrian , it is kind of, but a quick way to just check the time consumption of a piece of code. Actually I briefly checked the dev tool's performance feature after reading your comment but found profile seems to have too much application level performance analysis. May be I have to check more tutorials to go in deeper. I would appreciate if you have any suggestions for the same. Thank You!

Adrian B.G. • Sep 10 '18 • Edited

Ok but how would that help you? Most of the time you want to optimize the app or the golden path (or a specific action). To do that you have to find the bottleneck first then optimize it.
The idea is that you do not know what to improve until you benchmark the entire app.

There is a scenario when you want to measure a piece of code, when you do unit benchmarks, when you want to improve an algorithm and compare two versions in paralell. But Im sure there are better ways to do this in JS, like benchmark.js, the lib behind jsperf.com

// add tests
suite.add('old', function() {
  yourOldFunction();
})
.add('new', function() {
  yourNewFunction();
})
.on('complete', function() {
  console.log('Fastest is ' + this.filter('fastest').map('name'));
})
// run async
.run({ 'async': false });

The idea is Not to modify your code, but rather test it from the outside.
You can add performance tracking in your TEST files, which will not be bundled in the production.

Also I forgot to mention, the HTML5 added a new API with this purpose, to measure the performance: developer.mozilla.org/en-US/docs/W...

var t0 = performance.now();
doSomething();
var t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.");

The difference is that console is a functionality added by the browser but the performance is a "native" tool.

Pranjal Agnihotri {..❤️} • Dec 19 '19

Hey @adrian , I want to just get the elapsed millisecond for a particular JS function in web-app, is there any simpler way to achieve this without using browser native API. Benchmark.js seems over kill for this use case.

varo manukyan • Sep 9 '18

Unfortunately, this kind of performance measurements are useless.

You can't measure the performance of the entire application
Every time you re-run it will produce completely different results, so you can't event say how long it will take a particular function to run.

Never rely on measurements like this one and better use browser dev tools, they're great!

Sanket Patel • Sep 10 '18 • Edited

Yes, I agree this is not something that can measure the performance of whole app, but as @dimpiax rightly said, can be useful just to check time consumption of the piece of code quickly.

I also appreciate the point you mentioned about the browser dev tool. I tried it after @bgadrian mentioned in a comment above. But in my brief experiment I found it with too much high level info, may be I need to check the official tutorials to get better idea. Would love to know if you have any reference. Thanks!

Dmytro Pylypenko • Sep 9 '18

In case of unit tests measurement – current approach is perfect.

Adrian B.G. • Sep 10 '18

Not really, is better to use a tool like benchmark.js and wrap your functions there, this way you avoid polluting your code and keep it away from the production bundles.

Dmytro Pylypenko • Sep 10 '18

It depends on skills of developer, if he cannot write vanilla simple functions and doesn't know how to organize architecture and behavior of application, which produces polluting – then developer starts to use 3rd party libraries for trivial purposes.
If developer is skilled – it's enough to wrap using native functions, like console.time and console.timeEnd.

For example:

const measure = (label, closure) => { 
    console.time(label); 
    closure(); 
    console.timeEnd(label); 
}

measure('one', () => { 
    Array.from(Array(10000), (_, i) => i).map(v => Math.random(v)); 
})

varo manukyan • Sep 10 '18 • Edited

Please note, every time you re-run it will produce completely different results, so you can't event say how long it will take a particular function to run.

Unlike console.time(), benchmark allows you to run you suits lots of times, giving your more correct average results.

Or you can test your units with jsperf.com/

Dmytro Pylypenko • Sep 10 '18

Of course, because processor allocates resources differently.
When we talk about measurement for unit tests or for performance function – time is the range of allowed min/max.

Adrian B.G. • Sep 10 '18

I agree, the dev must know what a framework does, but framework or vanilla, the LOC used to benchmark (like performance or console) would be better to be in separate .js files, which are not bundled into the product.