What are the methods of code optimization for mob. devices?

Question

JavaScript

I'll start by saying that I'm a debutant in app development for mob. devices. I always wanted to check, I saw a lot of applications and games written in html5, with good rendering performance and other things, since I'm just a web developer, I decided to write a small game in html5 using the quintus framework .
As a builder, I used phonegap, but without its api and functions, just as a compiler.
And I noticed that the animation and the 2d game itself "slows down" a little, because of what it could be, and are there any methods for optimizing the code for the mob. devices.
Also on the website of the framework developer, I noticed that the framework is used to create a mob. applications - html5quintus.com