Problem with document.forms[i][j].type, returns undefined

I'm writing a firefox addon. Here is a part of the quote

var cForm = ''; 
var doc = document;
for (i = 0; i < doc.forms.length; i++)
{
    var a = doc.forms[i].name + "";
    if ( a.search("itsMe") != -1)
    {
        cForm = i;
    }
}

//

if ( cForm != '' )
{
    for (i = 0; i < doc.forms[cForm].length; i++)
    {
        var sTotal = 'doc.forms[' + cForm + '][' + i +'].type';             
        if ( eval(sTotal) == "button")
        {
            return sTotal ;
        } 

    }
}

The first code works well. The 2nd code sho开发者_如何转开发ws an error like: "doc.forms[0][0] is undefined"

whats wrong?? help...

The issue could be in your use of eval; it might not know about doc, since it's not in scope. In general, you should try to avoid using eval. You really don't need it in this case, so try doing something like this:

if (i.length && typeof(cForm) != "undefined")
{
    cForm = parseInt(cForm);
    for (i = 0; i < document.forms[cForm].length; i++)
    {
        if (document.forms[cForm][i].type == "button")
        {
            return sTotal ;
        } 

    }
}

doc.forms[0][0] could be a textarea, say, which would make it have no .type.

On a separate note, why are you using eval, exactly???