Effect of jQuery and jQuery Mobile on PhoneGap/Cordova Startup Speed

App load time can have a significant effect on how users perceive your app (see these articles). While load time of Cordova apps is a complex thing made up of multiple steps, one (possibly big) part of it is loading all the JavaScript and CSS resources on the initial HTML page.

An often used framework for mobile apps is jQuery Mobile. Just look at the "related tags" statistics on Cordova questions on StackOverflow. Such libraries are useful for beginners. Lately, though, I have been trying to write plain JavaScript without libraries. To validate the performance gains from this approach, I wanted to see how much using jQuery and jQuery Mobile affect the load time of an app.

Measurements

I originally measured with four devices: iPhone 3GS, iPhone 4S, iPad 2, and 3rd generation iPad. While I procrastinated writing this post, new devices were released (and bought). So I made additional measurements on iPhone 5S and retina iPad Mini as well.

In all measurements, I used Cordova 3.0 (although 3.1 3.2 3.3 is already released). I had the console plugin installed, but no other plugins. The template I used was a stripped down version of the default project template (see this gist for the complete HTML I used). I had three versions:

  • without any JavaScript libraries, only loading cordova.js
  • with cordova.js and jQuery 2.0.3
  • with cordova.js, jQuery 1.9.1, and jQuery Mobile 1.3.2 (including CSS and JavaScript)

The versions of jQuery and jQuery Mobile are the latest versions at the time of making the first measurements.

I measured the time between a script element in the beginning of head and the deviceready event to fire (as you can see from the template). With each device, I measured every version 10 times to get more reliable data.

Results

The results are summarised in the figure below. The raw data is also available.

measurements.png

The results show no real difference between iOS 5 and 7 on iPad 2 and between iOS 6 and 7 on 3rd generation iPad. Neither is there much difference between those two devices. iPhone performance has clearly improved in newer devices. The same is true for iPad Mini. Nothing surprising in that, though.

What is notable is that jQuery Mobile does affect the start-up time of the application quite significantly. In most devices, it takes around 0.5s for the deviceready event to trigger. And over 0.4s even on the latest iPhone, not to mention the over a second on 3GS.

Take Aways

So what can we learn from the results? I’d say that if you target older versions of iOS which run on 3GS (or, perhaps iPad 1), you should think long and hard before you adopt a large library like jQuery Mobile. If you still device to go with jQuery Mobile (or similar libraries), the load speed of the app could (and should) be improved by loading the libraries after deviceready. Also, I used the complete library, and you should definitely build your custom version with only the needed components.

Another alternative is to use more lightweight frameworks such as Zepto + Topcoat. The fastest approach, performance wise, is writing JavaScript and CSS without libraries. If you are not comfortable with that, now might be a good time to learn.

All in all, just keep in mind that half a second can feel like a long time and can have an effect on your app ratings and business performance. On the other hand, if you do a lot of other processing on startup, the JavaScript loading times might not be a significant factor in app startup.

Conclusion

As with most questions in software development, my suggestion whether or not to use libraries in Cordova apps is “it depends”. It is a balance between app load performance and developer productivity. Just keep in mind that the libraries you use can have a big impact on load times. Personally, while I do have an app in the app store (published by my previous company) that uses jQuery Mobile, I would not use it in a new project.

What do you think? Do you use libraries in your Cordova apps?

Update: If you read this far, you might also want to check out the post about whether you should minify your resources in a Cordova/PhoneGap app.


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