[whatwg] Script preloading: Browser Pre-compiled Scripts Cache?

[Boris Zbarsky]

On 7/15/13 3:42 AM, Bruno Racineux wrote:
> Wouldn't browsers be able to store "pre-parsed/compiled' scripts in a
> separate "byte code" cache,

You mean like https://bugzilla.mozilla.org/show_bug.cgi?id=679942 ?

There's some discussion in there about whether this is a worthwhile 
optimization with modern JS engines, which feature lazy compilation and 
even lazy parsing to a large extent....  Measurement is needed of the 
various pieces discussed in 
<https://bugzilla.mozilla.org/show_bug.cgi?id=679942#c6> and 
<https://bugzilla.mozilla.org/show_bug.cgi?id=679942#c7>.

In either case, note that there is already caching of this sort to some 
extent in SpiderMonkey; see 
https://bugzilla.mozilla.org/show_bug.cgi?id=883154 which is fixed. 
Note that in the context of that bug a "script" is what you probably 
think of as a "function body": that's the fundamental unit of 
compilation in SpiderMonkey now that we do lazy compilation.

> i.e. Why do we have to keep re-parsing and re-evaluating the very same
> scripts, especially CDN libraries and social apis largely shared among
> websites, over and over?

The re-evaluating is because evaluation has little things like 
side-effects.  ;)

> the whole parse/evaluation time, could be cut 'partially', yet very significantly

Some hard data would be useful here, as I said above.

-Boris