I have a currently fairly dysfunctional Javascript program that's been causing me problems. However, it throws one error that I just don't understand:

TypeError: 'undefined' is not an object (evaluating 'sub.from.length')

What I'm trying to do, as you can probably guess, is check the length of a certain from array in the sub dict. Here's the source code for the entire function, and here's the code of the loop that I think is causing the error:

console.log(afcHelper_ffuSubmissions.length); // just for debugging, returns the correct number

for (var i = 0; i < afcHelper_ffuSubmissions.length; i++) { // this whole section works fine

    var sub = afcHelper_ffuSubmissions[i];

    //console.log(THIS IS BROKEN DOWN BY LINK,afcHelper_Submissions[i]);

    if (pagetext.indexOf(afcHelper_ffuSections[sub.section]) == -1) {

        // Someone has modified the section in the mean time. Skip.

        document.getElementById('afcHelper_status').innerHTML += '<li>Skipping ' + sub.title + ': Cannot find section. Perhaps it was modified in the mean time?</li>';

        continue;

    }

    var text = afcHelper_ffuSections[sub.section];

    var startindex = pagetext.indexOf(afcHelper_ffuSections[sub.section]);

    var endindex = startindex + text.length;



    console.log(sub); 

    if (typeof(sub.from) != 'undefined' && sub.from.length > 0) { // ** problem spot?? this is the code i recently added.

        for (var i = 0; i < sub.from.length; i++) {

            mainid = sub.from[i]['id'];

            var sub = afcHelper_Submissions[mainid]; // and then it goes on from here...

Any ideas would be great. Frankly, I just can't see why I'm getting a TypeError about something that I've already explicitly checked the type of (typeof(sub.from))...