Originally published at: http://www.sitepoint.com/improve-javascript-performance-analysis-results-user-marks/
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When working on advanced JavaScript code, like a 3D engine, you may ask yourself what you can do to optimize performance, and how much time you should spend working on specific pieces of code. In this tutorial, I’ll share several tools that provide insight into how your code is performing, and show you how to make the most of user marks in the memory graph to analyze your performance.
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Need a profiler?
One that comes to mind is the integrated profiler you can find using the new updates to the Internet Explorer F12 Dev Tools, enhancements that will also be available for Project Spartan. Of course, you can use any similar tools you prefer too on your dev box. If you want to try this out on Android, iOS, or Mac OS, you can also use remote.IE to get an instance of Windows 10 Technical preview running in minutes. Then open the Internet Explorer “e” you’ve been avoiding (it is a temporary client shell that has Project Spartan’s new rendering engine configured), hit “F12” and now you can see what I’ll show you:
Please note that with the new F12 tools that we shipped with Windows 10 Technical preview, profiler is now part of the UI responsiveness window:
Let’s see other options that can give you more insights about how your code is performing.
console.time
You just have to call console.time() and console.timeEnd() around the piece of code you want to evaluate. The result is a string in your console displaying the time elapsed between time and timeEnd.
This is pretty basic and can be easily emulated but I found this function really straightforward to use.
Even more interesting, you can specify a string to get a label for your measurement.
This is for instance what I did for Babylon.js:
console.time("Active meshes evaluation");
this._evaluateActiveMeshes();
console.timeEnd("Active meshes evaluation");
This kind of code can be found around all major features and then, when performance logging is enabled, you can get really great info:
Be warned that rendering text into the console can consume CPU power
Even though this function is not standard, browser compatibility is pretty great, with Chrome, Firefox, IE, Opera and Safari all supporting it.
Performance object
If you want something more visual, you can use the performance object as well. Among other interesting features to help you measure a web page’s performance, you can find a function called mark that can emit an user mark.
A user mark is the association of a name with a time value. You can measure portions of code with this API in order to get precise values. You can find a great article about this API by Aurelio de Rosa on SitePoint.
The idea today is to use this API to visualize specific user marks on the UI Responsiveness screen:
This tool allows you to capture a session and analyze how CPU is used:
We can then zoom on a specific frame by selecting an entry called Animation frame callback and right-clicking on it to select filter to event.
The selected frame will be filtered then:
Thanks to the new F12 tool, you can then switch to JavaScript call stacks to get more details about what happened during this event:
The main problem here is that it is not easy to get how code is dispatched during the event.
This is where user marks enter the game. We can add our own markers and then be able to decompose a frame and see which feature is the most expensive and so on.
Continue reading this article on SitePoint