Validate a checkbox

I have created a form that requires checking a box certifying that you agree to terms.

Code:

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<input name="certify" type="checkbox" value="Y" ID="CertChkbox"/>

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This is the last item on the form which contains mostly address info. I then added the following javascript:

Code:

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<script>
function validateForm()
{
       
var x=document.forms["PledgeForm"]["FirstName"].value;
if (x==null || x=="")
  {
  alert("First name is a required field and must be completed");
return false;
  }
var x=document.forms["PledgeForm"]["LastName"].value;
if (x==null || x=="")
  {
  alert("Last name is a required field and must be completed");
return false;
  }


this goes on for a few more fields and then I tried adding the following code for  the checkbox:

if (PledgeForm.Certify.value == null)
{
        alert("error message");
}

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I am not sure what I am doing wrong. How can I validate the checkbox?

Thanks in advance.

First off, never do client-side form processing if security is an issue at all. Anyone can disable or change JavaScript through their browser. The server-side scripts cannot be altered by the client.

Second, if you're going to stick with JavaScript, checkboxes just return either true or false. It's as simple as that!

Code:

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if (document.forms["PledgeForm"]["Certify"].checked) {...}

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