Question

I’m writing a recursive function in JS and having some trouble. Let’s start with this very basic function:

function traverse(thing)
{
    if (typeof traverse.depth == 'undefined')
        traverse.depth = 1;
    else
        traverse.depth ++;

    if (thing.child)
        traverse(thing.child);
}

So this works fine, and depth acts as a static var of sorts, but the problem is that in a language like C that has proper static vars, as you back out of the function, this variable would (ostensibly) decrease, so it is a true depth. If I have three boxes that contain three boxes and each of those contain three boxes, etc., we’re essentially drilling down into the deepest one till there are no children, then backing out up a level to a sibling, and traversing its children. The problem with the above code is that the depth keeps increasing and increasing infinitely, even though the TRUTH depth may only be 3 or 4 from the oldest ancestor to the youngest child. If there are 80 siblings on each level, that depth counter is going to skyrocket.

How do I keep track of true depth in JS recursive functions?

Answer 1

Don’t attach the counter to the function. The counter is shared by all recursive calls, so the counter represents the number of function calls, instead of the recursion depth.

When depth is passed as a separate variable, the counter shows the true depth.

function traverse(thing, depth)
{
    if (typeof depth == 'number')
        depth++;
    else
        depth = 1;

    if (thing.child)
        traverse(thing, depth);
}