Most web applications have to talk to a third party API that they don’t control and didn’t write. A good strategy for dealing with that library is to have all your access to the library go through a wrapper object.
When you use a wrapper object, you can define the wrapper object in terms that are semantically relevant to your application. It also becomes easier to test your application, because you can test it as far as the wrapper and then test the wrapper's interaction with the API separately. It’s also easier to change the library if needed.
Those features are valuable in front-end development, too. However, many front-end applications intertwine with the DOM or with a library like jQuery in a way that can make the code extremely dependent on the specifics of one particular page setup.
In this XI to Eye video tutorial I walk through the process of treating jQuery and the DOM like a third-party library, and creating a wrapper object to manage interaction with the DOM.