JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

Note that this isn‘t a terribly robust function—if you pass it strings or other data types that
shouldn‘t be added, it will try to sum those as well. We‘ll see more sophisticated uses of
functions taking a variable number of parameters when we present various JavaScript
applications later in the book. We will also see functions used as objects starting in the next
chapter. For now, let‘s turn our attention to a special technique used in creating functions—
recursion.
Recursive Functions
A recursive function is one that calls itself. While not always the most efficient execution (timewise)
way to perform a computation, the elegance of a recursive function is very appealing.
Many programmers find the simplicity with which some computation can be expressed in a
recursive fashion to outweigh the disadvantage of the overhead incurred by repeated function
invocation.
Consider the definition of factorial from mathematics, where given a number n,
n! = n* (n–1) * (n–2) * … * 1
So, given this definition of factorial, 5! = 5 * 4 * 3 * 2 * 1, or 120. For completeness, 0! is defined
to be 1, and factorial of negative numbers is not defined. We could write a recursive function to
calculate the factorial in a somewhat naïve fashion. Here, the function factorial keeps calling
itself with smaller and smaller values until the base case of 0 is hit, at which point the results
are returned ―upward‖ until the calculation is complete.
function factorial(n)
{
}
if (n == 0)
else
return 1;
return n * factorial(n-1);
Passing the function a positive value, we see that
alert(factorial(5));
produces the desired result:
However, if a negative value is passed to the function, the recursion will continue indefinitely.
Notice the error produced by Internet Explorer in such a case: