[whatwg] Proposal for separating script downloads and execution

Kyle Simpson getify at gmail.com
Tue Feb 8 16:31:59 PST 2011

?> Isn't this just a quality of implementation issue?

No, frankly it isn't. No matter how good the implementation of the 
JavaScript engine on mobile, the mobile device will always be much more 
limited in processing power than a desktop browser environment. There are 
those who think that the mobile and desktop paradigms are not (or shouldn't 
be) fundamentally different in some respects, but those people are 

Mobile will always have special challenges that desktop may not face. And 
the faster that mobile devices get, the more complex the scripts that devs 
will want to shove down the pipes to run on it. You can't just wait around 
for some mythical future time when mobile processing power is not a limiting 
factor. The fact is, it's a limiting factor right now, and will be for any 
foreseeable future. And so we're trying to find ways to juggle the costly 
operations around to help mitigate the impact.

It's also tempting to just get mired down in this one use-case of mobile 
JavaScript parsing deferral. While this use-case is a great example of why 
controlling execution is important, there are plenty of other use-cases for 
loading a script ahead of time and not using the script (parsing/executing 
it) until later (or sometimes never).


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