ilyo - 1 year ago 57
Javascript Question

# How exactly does this recursive function work in JavaScript?

I have the following example of a recursive function, and what I don't understand is the order in which things are happening:

``````function power(base, exponent) {
if (exponent == 0)
return 1;
else
return base * power(base, exponent - 1);
}
``````

When does the function return the values, at the end of all the process or each time?

A simple way to visualize what happens in recursion in general is this:

1. a stack of calls to the function is created: this process needs a proper termination condition to end (otherwise you'll have infinite recursion, which is evil)
2. the single results are popped out of the stack: each result is used to calculate the next step, until the stack is empty

I.e. if base=5 and exponent=3, the call stack is (last element on top):

``````5*(5*(5*1))
5*(5*(5*power(5, 0)))
5*(5*power(5, 1))
5*power(5, 2)
power(5, 3)
``````

then every called function has real parameters and is ready to return a value (first element on top):

``````5*(5*(5*1))
5*(5*5)
5*25
125
``````

Note that here the functions are calulated in inverse order: first `power(5, 0)`, then `power(5, 1)`, and so on.. After each calulation an element of the stack is released (i.e. memory is freed).

Hope it helps :)