Enable/Disable submit button if checkbox is checked/unchecked?

Question

How to enable the submit button in my HTML form and disable if checkbox was unchecked?

What is wrong with this code?

EnableSubmit = function(val)
{
    var sbmt = document.getElementById("Accept");

    if (val.checked == true)
    {
        sbmt.disabled = false;
    }
    else
    {
        sbmt.disabled = true;
    }
}                       

The check box

<td width="30%">Do you accept Terms of Service agreement?</td>
<td width="10px" style="min-width: 10px"></td>
<td width="70%">
    <input type="checkbox" name="TOS" value="Accept" onClick="EnableSubmit"> I agree to Terms of Service agreement.
</td>

Answer 1

Change your HTML to this:

<td width="30%">Do you accept Terms of Service agreement?</td>
<td width="10px" style="min-width: 10px"></td>
<td width="70%">
    <input type="checkbox" name="TOS" value="Accept" onClick="EnableSubmit(this)"> I agree to Terms of Service agreement.
</td>

Reason it's not working: you're not passing your function anything. Actually, because you've not used parentheses with the function name, you've not called the function at all. Passing it this in the context of the onclick HTML event attribute means you're passing a reference to the element's DOM object, giving you access to its checked property.

Answer 2

You need to include the parameters: onClick="EnableSubmit()"

 <input type="checkbox" name="TOS" value="Accept" onClick="EnableSubmit()"> I agree to Terms of Service agreement.