Form Array Checkbox Accesing

First I'm sure the answer to ths JS question is buried somewhere in the many item of this forum. Just could not find it. So I'm working on changes to a form developed by someone else. In the form the previous developer wrote the following:

<input type="checkbox" name="method[]" value="payroll_onetime">Payroll
<input type="checkbox" name="method[]" value="payroll_onetime">One-time
<input type="checkbox" name="method[]" value="paper">Paper Check
<input type="checkbox" name="method[]" "onlinebill">Online Bill

Note there are other form and HTML I removed.

So my problem is this. I'm trying to access the method checkbox array from a JS function. So I write:

function setPayrollStatus()
{
alert(document.profile.method.length);
}

This does give me that value of 4. Since there are 4 checkboxes for method I'm thinking this is correct. So next I add:

for (var idx=0; idx < document.profile.method.length; idx++)
{
alert(document.profile.method[idx].checked);
}

Now I get only 'undefined'.

What I want to accomplish is to check the first item. I thought I would be able to write something like: document.profile. method[0].checked = true;

If I change the form name tags from 'method[]' to 'method' it works. Problem is he also wrote the php back end processing for this form. And in PHP this syntax yeilds an array for the method vriable.