What's wrong with my JavaScript Search Recursive Loop?

Question

I can't seem to figure out why my recursive search will not behave recursively.

Do you see what's wrong? Do I have a haystack[i] in the wrong place? Because I am not seeing it. I've tried looking through examples on this site but I can't figure out something so simple.

search = function(needle, haystack) {

    len = haystack.length;
    for (var i = 0; i < len; i++)
    {
        if (typeof haystack[i] == 'object') {
            search(needle, haystack[i])
        } else {
            if (needle == haystack[i]) {
                console.log('found');
                return;
            }
            console.log('value: ' + haystack[i])
        }
    }
}

var test = [[1], [2], [3,4], [5,6]]
search(4, test)

Or see the fiddle @ http://jsfiddle.net/aniyishay/TBMmK/ (Open the Console)

Arun P Johny · Accepted Answer · 2013-08-22 03:10:43Z

3

You are missing var in front of len, it should be var len = haystack.length; otherwise it is treated as a global variable.

when haystack = [[1], [2], [3,4], [5,6]] then len = 4 but again search(4, [1]) is called then len = 1 is assinged then when the loop is returned the value of len = 1 instead of the original 4 because it is a global variable. Now i =2 and len = 1 so the loop exists

answered Aug 22, 2013 at 3:10

Arun P Johny

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4 Comments

Arun P Johny Over a year ago

@Doorknob yes it will... did you test it

tckmn Over a year ago

Hm. That's interesting, why is that? (+1) Why does changing the global variable to a local one matter?

Jonathan Lonowski Over a year ago

@Doorknob After the 1st recursive call, len will be set to 1 ([1].length). Returning to the original call, i < len will be false as i++ will set i to 1 as well, ending that loop and preventing further searching. Scoping len allows it to remain set to 4 for the 1st call.

JREAM Over a year ago

Thanks so much, that makes sense. I couldn't even think of that being the problem, great find thanks so much!

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