Question

My latest project is using a javascript framework (jQuery), along with some plugins (validation, jquery-ui, datepicker, facebox, …) to help make a modern web application.

I am now finding pages loading slower than I am used to. After some js profiling (thanks VS2010!), it seems a lot of the time is taken processing inside the framework.

Now I understand the more complex the ui tools, the more processing needs to be done. The project is not yet at a large stage and I think would be average functions. At this stage I can see it is not going to scale well.

I noticed things like the ‘each’ command in jQuery takes quite a lot of processing time.

Have others experienced some extra latency using JS frameworks?
How do I minimize their effect on page performance?
Are there best practices on implementation using JS frameworks?

Thanks

Answer 1

My personal take is to use the framework methods and tools where they make sense and make life easier, for example selectors and solving cross-browser quirks, and to use plain old vanilla JavaScript where there is no need to use the framework methods, for example, in simple loops.

I would check and double check the code that you have that uses the framework to ensure that it will perform as well as it can; it is all too easy to use a framework in a poor performing fashion and sometimes one doesn’t discover this until one profiles it 🙂

Frameworks do introduce extra latency as there are usually a number of functions that are executed as a result of using the entry point function into using them.

EDIT:

Some general points with regards to using jQuery:

1.cache your jQuery objects in local variables if you are going to use them more than once. Querying the DOM is a relatively expensive operation and therefore should be done as little as is needed. If you have related selectors, take a look at performing a wide selection and then using the methods such as find(), filter() next(), prev() etc to filter the collection to get the relevant elements that you would have usedanother selector function to get.

2.Inside of functions, don’t wrap objects in jQuery objects unneccessarily. If there is a cross browser way of accessing an object property value that is reliable, then use that. For example, the value property of a text input HTMLElement

$('input:text').each(function() {
    // use
    this.value

    // don't worry about this
    $(this).val();
 }); 

3.Try to avoid adding large script files where you’re using only a small piece of the functionality. There can be a lot of time spent parsing and executing code on page load that you’re never going to use! If possible, extract only the relevant code that is needed. I appreciate that this can be hard and is not always possible, particularly when it comes to versioning, but it’s worth pointing out nonetheless.