JavaScript-multiple checkbox validation not work

Question

I have a form

<form method="post" action="" onsubmit="validate()">
<input type="checkbox" name="del[]" value="1">
<input type="checkbox" name="del[]" value="2">
<input type="checkbox" name="del[]" value="3">
<input type="checkbox" name="del[]" value="4">
<input type="checkbox" name="del[]" value="5">
<button type="submit" class="btn btn-danger btn-lg">delete</button>
</form>

i try to do checkbox validation with JavaScript,if people not select a check box,it will show a message,if people select one or more than one check box, it will show the confirm alert to confirm submit.But my JavaScript is not work. The form will submit without validation.

    <script>
    function validate() {
        var checkbox=document.getElementsByName("del[]");
        if (checkbox.checked == null || x == "") {
            alert("Please select!");
            var check=false;
            return false;
        }

        if(check != false && !confirm('confirm submit?')){
            e.preventDefault();
            return false;
        }
        return true;
    }
   </script>

How can i fix the problem?

Answer 1

Something like this will make sure at least one check box is checked

 document.getElementById('myform').onsubmit = function (e) { var checkbox = document.getElementsByName("del[]"), i, checked; for (i = 0; i < checkbox.length; i += 1) { checked = (checkbox[i].checked||checked===true)?true:false; } if (checked == false) { alert('Check Something!'); e.preventDefault(); return false; } else if(confirm('confirm submit?')) { alert('done!'); return true; } } 

 <form id="myform"> <input type="checkbox" name="del[]" value="1"> <input type="checkbox" name="del[]" value="2"> <input type="checkbox" name="del[]" value="3"> <input type="checkbox" name="del[]" value="4"> <input type="checkbox" name="del[]" value="5"> <button type="submit" class="btn btn-danger btn-lg">delete</button> </form> 

Answer 2

getElementsByName returns a collection of objects. That collection does not have a checked property, so this fails:

var checkbox = document.getElementsByName("del[]");
if (checkbox.checked == null ...  //error, no "checked" property

A simple alternative would be to use document.querySelector to look for a single checked input:

function validate() {
  var checkbox= document.querySelector('input[name="del[]"]:checked');
  if(!checkbox) {
    alert('Please select!');
    return false;
  }
  else return confirm('confirm submit?');
}

Also, change this:

<form method="post" action="" onsubmit="validate()">

… to this:

<form method="post" action="" onsubmit="return validate()">

Fiddle

Answer 3

Another Simple way is to create & invoke the function validate() when the form loads & when submit button is clicked. By using checked property we check whether the checkbox is selected or not. cbox[0] has an index 0 which is used to access the first value (ie 1) with name="del[]"

You can do the following:

 function validate() { var cbox = document.forms["myForm"]["del[]"]; if ( cbox[0].checked == false && cbox[1].checked == false && cbox[2].checked == false ) { alert("Please Check Something"); return false; } else if (confirm("Confirm Submit?")) { alert("Successfully Submited"); return true; } } 

 <form onload="return validate()" name="myForm"> <input type="checkbox" name="del[]" value="1"> 1 <input type="checkbox" name="del[]" value="2"> 2 <input type="checkbox" name="del[]" value="3"> 3 <input type="checkbox" name="del[]" value="4"> 4 <input type="checkbox" name="del[]" value="5"> 5 <br> <input type="submit" value="Delete" onclick="validate()"> </form> 

Demo: CodePen