performance - How big are JavaScript function objects?

Question

I was just wondering how the overhead is on a function object.

In an OOP design model, you can spawn up a lot of objects each with their own private functions, but in the case where you have 10,000+, these private function objects, I assume, can make for a lot of overhead.

I'm wondering if there are cases where it would be advantageous enough to move these functions to a utility class or external manager to save the memory taken up by these function objects.

Answer 1

This is how Chrome handles functions, and other engines may do different things.

Let's look at this code:

var funcs = [];
for (var i = 0; i < 1000; i++) {
    funcs.push(function f() {
        return 1;
    });
}
for (var i = 0; i < 1000; i++) {
    funcs[0]();
}

http://jsfiddle.net/7LS6B/4/

Now, the engine creates 1000 functions.

The individual function itself takes up almost no memory at all (36 bytes in this case), since it merely holds a pointer to a so-called SharedFunctionInfo object, which is basically a reference to the function definition in your source code*. This is called lazy parsing.

Only when you run it frequently does the JIT kick in, and creates a compiled version of the function, which requires more memory. So, funcs[0] takes up 256 bytes in the end:

_{*) This is not exactly true. It also holds scope information and the function's name and other metadata, which is why it has a size of 592 bytes in this case.}