[RESOLVED] JavaScript Recursion Not Working

Bonesnap

I'm implementing a shuffle feature for my music player. When the shuffle mode is turned on and a song ends, it chooses a random number from 0 to the number of songs that are available (inclusive). So the first listed song is 0, second is 1, and so on.

The random part is working correctly, however, I have added a little bit of extra code to check if the number/index chosen is the same as the song that is currently playing, so it doesn't play the same song twice (or more) consecutively. To accomplish this I made my function recursive; however, whenever the value is the same, it doesn't call the function again. It simply stops.

function shuffle_song(i)
{
    var value = Math.floor(Math.random() * ($('div.search-result:visible').length));

if(i == value)
{
console.log(i);
console.log(value);
shuffle_song(value);
}
else
{	
return value;
}
}

I put in some console.log() calls for debugging. They are called successfully in Firebug but the function is not called again. There are no other errors in Firebug either. Am I doing something wrong with recursion, or am I missing something entirely?

Thanks for any help!

Bonesnap

Quick follow up: Inserting a console.log() right at the start of the function reveals that the function is indeed called, but it is apparent nothing else happens.

Bonesnap

I realized that I wasn't returning from the second function call. I also removed the else portion from the return statement. Hurray for debugging!

function shuffle_song(i)
{
    var value = Math.floor(Math.random() * ($('div.search-result:visible').length));

if(i == value)
{
value = shuffle_song(value);
}

return value;
}

Weedpacket

Since it's pure tail recursion the recusion is unnecessary (everything pushed onto the call stack is simply thrown away as soon as it is popped):

function shuffle_song(i)
{
	var value;
	do {
		value = Math.floor(Math.random() * ($('div.search-result:visible').length));
	} while(i == value);
	return value;
}

And then of course that length can be pulled out of the loop into a temporary variable so that it doesn't get recomputed every time.

Bonesnap

Ah, thank you for that! I originally wanted to do it in a loop but couldn't wrap my head around it and figured I haven't done recursion in JavaScript before so what the hell. I've changed it to the loop now. I have also added a check to see if the length is only one and to just return the original index to avoid an endless loop.