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By now, most mainstream browsers have started integrating optimizing JIT compilers to their JavaScript interpreters/virtual machines. That's good for everyone. Now, I'd be hard-pressed to know exactly which optimizations they do perform and how to best take advantage of them. What are references on optimizations in each of the major JavaScript engines?
Background:
I'm working on a compiler that generates JavaScript from a higher-level & safer language (shameless plug: it's called OPA and it's very cool) and, given the size of applications I'm generating, I'd like my JavaScript code to be as fast and as memory-efficient as possible. I can handle high-level optimizations, but I need to know more about which runtime transformations are performed, so as to know which low-level code will produce best results.
One example, from the top of my mind: the language I'm compiling will soon integrate support for laziness. Do JIT engines behave well with lazy function definitions?
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Optimization is a special type of JavaScript minification. These kind of minimizers not only delete unuseful white spaces, commas, comments etc. but also help to avoid “dead code”: Google Closure Compiler.
A JavaScript engine is a computer program that executes JavaScript code and converts it into computer understandable language.
However, V8 does it incrementally, i.e., for each GC stop, V8 tries to mark as many objects as possible. It makes everything faster because there's no need to stop the entire execution until the collection finishes. In large applications, the performance improvement makes a lot of difference.
That's why it is so essential to implement objects with the same properties in the same order to have the same hidden class. Otherwise, V8 won't be able to optimize your code. In V8 words, you want to stay as much monomorphic as possible.
This article series discusses the optimisations of V8. In summary:
The first two points might not help you very much in this situation. The third might show insight into getting things cached together. The last might help you create objects with same properties so they use the same hidden classes.
This blog post discusses some of the optimisations of SquirrelFish Extreme:
TraceMonkey is optimised via tracing. I don't know much about it but it looks like it detects the type of a variable in some "hot code" (code run in loops often) and creates optimised code based on what the type of that variable is. If the type of the variable changes, it must recompile the code - based off of this, I'd say you should stay away from changing the type of a variable within a loop.
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I found an additional resource:
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