Javascript Checkbox Loop Error

Firebug gives me an undefined error, when it's clearly defined.

[code junkie8]

Alright, I made a function to get the values of checked checkboxes to collect and in further development of the function, I will pass data through AJAX.

Anyways, continuing on, here's my function:

function generate_email (form_name, field_name, type) {
  var check_box_field = document.forms[form_name].elements[field_name];
  var check_box_count = check_box_field.length;
  var user_ids;
  
  for (var i = 0; i <= check_box_count; i++) {
    if (check_box_field[i].checked) { //
      if (check_box_count != (i + 1))
        user_ids += check_box_field[i].value + ",";
      else
        user_ids += check_box_field[i].value;
    }
  }
}

The error that Firebug generates is:

check_box_field[i] is undefined
 - user_ids += check_box_field[i].value + ","; 

Thanks in advance!

- code_junkie8

[Fotiman]

Welcome to WebmasterWorld!

Your for loop is incorrect. You have:

for (var i = 0; i <= check_box_count; i++) {

It should be:

for (var i = 0; i < check_box_count; i++) {

Otherwise, when i == check_box_count you then if you try to access check_box_field[i] you will be stepping past the end of the array. An array of 10 items is accessed using indexes 0 through 9, so if you try to access it with index 10, you've gone too far.

Hope that helps.

[code junkie8]

Awesome, that fixed it. I had "var i = 1;" at first because of the count's max number, but I thought, "Hey, that's dumb because arrays start at 0" and I never changed it back. Thanks Fotiman! :)