Instead of having V8 compile JavaScript on the fly and then execute it, isn't it possible to just compile the JavaScript beforehand and then embed the machine code in the page instead of embedding JavaScript in the page?
The way I understand it, the V8 JavaScript engine compiles to machine code anyway so why not just do it beforehand?
According to the W3C HTML5 Scripting specification, there's no standards-based reason why a browser couldn't support machine code with special type attributes (as Chrome does with the Dart language):
The following lists the MIME type strings that user agents must recognize, and the languages to which they refer:
"application/ecmascript" "application/javascript" ...User agents may support other MIME types for other languages...
Currently, no browser has implemented such a feature.
I suspect the primary shortcoming of such an approach is that each chip architecture would require a machine-code version of the script compiled for it specifically. This means that in order to support three architectures, a page would need to include a compiled script three times. (And it should be included a fourth time, as plain JavaScript, as a fallback for architectures that you didn't include, or for browsers that can't/don't support compiled code.) This could significantly bloat the size of the page with data that is mostly useless. The increase in load time would seem to significantly offset or completely outweigh whatever time you save on compilation.
An architecture-independent compromise solution like bytecode seems pretty poor: you still need to include the script twice (once for the bytecode, once normally for scripts that don't support it) and you need to do some kind of run-time processing on the bytecode to turn it into machine code.
The multiple-includes-with-fallback problem is exactly why other scripting languages have not made it into the Web environment: they would need coordinated cross-vendor support to be useful. Google is trying with Dart, but it remain to be seen what degree of success they see.
Note that Chrome does cache compiled versions of scripts so a script only needs to be compiled once and then the compiled code is cached for reuse when the user re-visits the page.