Javascript: Iterating over an array causes an infinite loop?

Question

I'm trying to iterate over some data in Javascript, using the following code:

for (var i = 0; i < fromdata.length; i++) {
    var mainid = fromdata[i].id;
    var sub = afcHelper_Submissions[mainid];
    /* do more stuff */

fromdata is an array of Objects that looks something like this:

[{ type="ffu", to=" Jon Corzine ", id=1, more...}, { type="ffu", to=" Jon Corzine ", id=2, more...}]

As you can see, I just want to get each object's id and store it to mainid and then do some more with it; however, I run into trouble: looping! Looping! Looping! The loop keeps running again and again. It never stops, and just manages to freeze up Firebug.

Update : Here's the "do more stuff", in all its pastebin glory: http://pastebin.com/Mfr90uq7 . Note that I changed the variable name from sub to sub_m to avoid a potential conflict, but the problem persisted.

Answer 1

A loop only can be infinite if the condition is always true. In your case it looks that it should reach a false , but provably formData is getting new elements each iteration of the loop or i is being modified and returned to previous values.

What I recomend is to create variables that will be used only for comparasion purposes:

var max = fromdata.length;
for (var count = 0; count < max; count++) {
    var i = count;
    // your stuff using formdata and i

Now max and count will not be modified by the code in the loop and the loop will reach an end.