Cost of calling a function or not in Javascript

Question

Compare:

if (myVariable) {
    doSomething()
}

function doSomething ()
{
    // Work goes here
}

vs

doSomething();

function doSomething()
{
    if (myVariable) {
        // Work goes here
    }
}

ie My question is whether it's faster to do the check outside of the function and avoid a context switch (I think that's the right term) ) or just do it inside the function because it makes such a minor difference?

Cheers.

Answer 1

It Just Doesn't Matter (although the first method avoids some work so it should faster, but by an amount which is probably less than statistical noise).

What really matters is which method best represents the logic. Rule of thumb is that every statement in a function should be on about the same level of abstraction. Is the conditional expression more or less abstract than the function call?

Answer 2

It would be faster to do it outside because making a function call every time will be slightly slower than checking first and then calling the function.

But why bother? No one is going to notice a function call vs what the function call is actually doing. Inefficient DOM selectors that make your code have to hunt and peck through a huge tree structure for a few needles in the haystack are a far greater threat to performance.