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?

Rick Hitchcock · Accepted Answer · 2015-04-10 18:20:40Z

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

edited Apr 10, 2015 at 18:20

answered Apr 10, 2015 at 18:14

Rick Hitchcock

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Comments

Downgoat · Accepted Answer · 2015-04-10 18:09:47Z

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>

aditya · Accepted Answer · 2018-08-25 15:23:36Z

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 (i.e 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

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