April 3, 2012

javascript multiple checkbox validation

Question by skylab

I would like to use this simple script with my form to make sure I have at least 1 box checked but I have a feeling something is wrong, most likely at the getElementsByName tag. I always get the pop up box no matter if I have items checked or not.

<script language="javascript">
function validate() {
    var chks = document.getElementsByName('id[][]');
    var hasChecked = false;
    for (var i = 0; i < chks.length; i++) {
        if (chks[i].checked) {
            hasChecked = true;
    if (hasChecked == false) {
        alert("Please select at least one.");
        return false;
    return true;

and the form, which may or may not end up with more checkboxes in the end:

name="form_type" onSubmit="return validate()">

<input id="attrib-8-10" type="checkbox" value="10" name="id[8][10]">
<label class="Checkbox" for="attrib-8-10">thick</label>
<input id="attrib-8-11" type="checkbox" value="11" name="id[8][11]">
<label class="Checkbox" for="attrib-8-11">medium</label>
<input id="attrib-8-12" type="checkbox" value="12" name="id[8][12]">
<label class="Checkbox" for="attrib-8-12">thin</label>

Answer by Starx

var chks = document.getElementsByName('id[][]');

Does not select any element, as you have specied all the index on the elements .

Here is how you can do it?

var chks= document.getElementsByTagName('input');
for (var x=0; x < chks.length; x++) {
    if (chks[x].type.toUpperCase()=='CHECKBOX' && chks[x].checked == true) {
        hasChecked = true;

Author: Nabin Nepal (Starx)

Hello, I am Nabin Nepal and you can call me Starx. This is my blog where write about my life and my involvements. I am a Software Developer, A Cyclist and a Realist. I hope you will find my blog interesting. Follow me on Google+


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