What are the performance effects of declaring functions inside functions?

Question

Suppose I have the following classes Test1 and Test2. Test1 declares two functions, fA and fB, and fA is called inside fB. Test2 declares fA inside fB. Would either of them have a performance advantage over the other? Assume that fA is recursive and will be called once every time fB is called.

Example:

function Test1() {
    this.fA = function() {
        //function body here...
    };

    this.fB = function() {
        //some code...

        this.fA();
    };
};

function Test2() {
    this.fB = function() {
        let fA = function() {
            //function body here...
        };

        //some code...

        fA();
    };
};

Unless the functions are going to be called millions and millions of times the difference is completely ignorable, if there's a difference at all. — Pointy
– Pointy, Commented Oct 1, 2019 at 15:44
There shouldn't be a notable performance differences if the function definitions are the same. — h0r53
– h0r53, Commented Oct 1, 2019 at 15:45
Note: the example provided is a typical use case for a prototype — BCDeWitt
– BCDeWitt, Commented Oct 1, 2019 at 15:52

Scott Hunter · Accepted Answer · 2019-10-01 15:46:00Z

1

In the first case, fA gets created once; in the second, it gets created each time fB is called. So the second is surely slower, but as @Pointy points out, probably not enough to worry about.

answered Oct 1, 2019 at 15:46

Scott Hunter

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