jquery validate check at least one checkbox

Example from https://github.com/ffmike/jquery-validate

 <label for="spam_email">
     <input type="checkbox" class="checkbox" id="spam_email" value="email" name="spam[]" validate="required:true, minlength:2" /> Spam via E-Mail </label>
 <label for="spam_phone">
     <input type="checkbox" class="checkbox" id="spam_phone" value="phone" name="spam[]" /> Spam via Phone </label>
 <label for="spam_mail">
     <input type="checkbox" class="checkbox" id="spam_mail" value="mail" name="spam[]" /> Spam via Mail </label>
 <label for="spam[]" class="error">Please select at least two types of spam.</label>

The same without field "validate" in tags only using javascript:

$("#testform").validate({ 
    rules: { 
            "spam[]": { 
                    required: true, 
                    minlength: 1 
            } 
    }, 
    messages: { 
            "spam[]": "Please select at least two types of spam."
    } 
}); 

And if you need different names for inputs, you can use somethig like this:

<input type="hidden" name="spam" id="spam"/>
<label for="spam_phone">
    <input type="checkbox" class="checkbox" id="spam_phone" value="phone" name="spam_phone" /> Spam via Phone</label>
<label for="spam_mail">
    <input type="checkbox" class="checkbox" id="spam_mail" value="mail" name="spam_mail" /> Spam via Mail </label>

Javascript:

 $("#testform").validate({ 
    rules: { 
        spam: { 
            required: function (element) {
                var boxes = $('.checkbox');
                if (boxes.filter(':checked').length == 0) {
                    return true;
                }
                return false;
            },
            minlength: 1 
        } 
    }, 
    messages: { 
            spam: "Please select at least two types of spam."
    } 
}); 

I have added hidden input before inputs and setting it to "required" if there is no selected checkboxes

Mmm first your id attributes must be unique, your code is likely to be

<form>
<input class='roles' name='roles' type='checkbox' value='1' />
<input class='roles' name='roles' type='checkbox' value='2' />
<input class='roles' name='roles' type='checkbox' value='3' />
<input class='roles' name='roles' type='checkbox' value='4' />
<input class='roles' name='roles' type='checkbox' value='5' />
<input type='submit' value='submit' />
</form>

For your problem :

if($('.roles:checkbox:checked').length == 0)
  // no checkbox checked, do something...
else
  // at least one checkbox checked...

BUT, remember that a JavaScript form validation is only indicative, all validations MUST be done server-side.

$("#idform").validate({
    rules: {            
        'roles': {
            required: true,
        },
    },
    messages: {            
        'roles': {
            required: "One Option please",
        },
    }
});

This is how I have dealt with it in the past:

$().ready(function() {                                                      
    $("#contact").validate({
        submitHandler: function(form) {
            // see if selectone is even being used
            var boxes = $('.selectone:checkbox');
            if(boxes.length > 0) {
                if( $('.selectone:checkbox:checked').length < 1) {
                    alert('Please select at least one checkbox');
                    boxes[0].focus();
                    return false;
                }
            }
            form.submit();
        }
    }); 

});

sir_neanderthal has already posted a nice answer.

I just want to point out that if you would like to use different names for your inputs you can also use (or just copy the method) require_from_group method from official jQuery Validation additional-methods.js (link to CDN for version 1.13.1).

It's highly probable that you want to have a text next to the checkbox. In that case, you can put the checkbox inside a label like I do below:

<label style="width: 150px;"><input type="checkbox" name="damageTypeItems" value="72" aria-required="true" class="error"> All Over</label>
<label style="width: 150px;"><input type="checkbox" name="damageTypeItems" value="73" aria-required="true" class="error"> All Over X2</label>

The problem is that when the error message is displayed, it's going to be inserted after the checkbox but before the text, making it unreadable. In order to fix that, I changed the error placement function:

if (element.is(":checkbox")) {
    error.insertAfter(element.parent().parent());
}
else {
    error.insertAfter(element);
}

It depends on your layout but what I did is to have a special error placement for checkbox controls. I get the parent of the checkbox, which is a label, and then I get the parent of it, which is a div in my case. This way, the error is placed below the list of checkbox controls.

make sure the input-name[] is in inverted commas in the ruleset. Took me hours to figure that part out.

$('#testform').validate({
  rules : {
    "name[]": { required: true, minlength: 1 }
  }
});

read more here... http://docs.jquery.com/Plugins/Valid...ets.2C_dots.29

 if ($('input:checkbox').filter(':checked').length < 1){
        alert("Check at least one!");
 return false;
 }