Are local function declarations cached?

Question

function A() {
     function B() {
          ...
     }        
     B();
}

Is function B created every time A is called or is there some caching on it. Is not making it local like :

function A() {
    B();
}
function B() {
    ...
}

A significant performance improvement?

Is it valid to do this a style choice? (B in this case is just a helper function for A.) or should the second be favoured for speed?

Should this style be used or avoided for readability?

Benchmark.

Seems like FF4 inlines B for the local case and removes the function call overhead.

What about other browsers?

Answer 1

Declaring an inner function in JS might have the purpose of being lexically bound to the outer function's local variables/arguments. Moving it out to be a top-level function defeats that purpose.

To answer the question: yes, the inner function is created every time, at least in theory, and this is how you should view it when writing the code, but a smart optimizer can still convert it to a top-level function, even if you have lexical dependencies. If it's a micro-optimisation, I wouldn't bother because having an inner function also serves the purpose of readability and declaring your intentions.