[JavaScript]: How to define a variable as object type?

Question

I am using following code to check whether a check box on my website page is checked or not. But there are several check boxes and I want to use this same function. I want to call this function from a Submit button click and pass the check box name as argument. It should than validate that check box.

function CheckTermsAcceptance()
{
    try
    {
        if (!document.getElementById('chkStudent').checked)
            alert("You need to accept the terms by checking the box.")  
            return false;   
    }
    catch(err)
    {
        alert(err.description);
    }
}

John Feminella · Accepted Answer · 2009-10-27 12:15:56Z

Just pass a parameter to CheckTermsAcceptance(). You also missed a brace after the alert -- there are two statements in that if block, and you'll always execute the return false without it.

function CheckTermsAcceptance(checkboxName)
{
    try
    {
        if (!document.getElementById(checkboxName).checked) {
                alert("You need to accept the terms by checking the box.")      
                return false;   
        }
    }
    catch(err)
    {
        alert(err.description);
    }
}

To call this from your submit button, have a function like validateForm that's called on submit. Then simply construct a list of the checkboxes and pass in their IDs to CheckTermsAcceptance.

Note that this sort of validation is handled very smoothly by jQuery and its ilk. For example, here's the jQuery validation plugin.

I think he's trying to call the function on submit. So what he also needs to do is scan the form for all check boxes and pass them one by one into the function.

Victor · Accepted Answer · 2009-10-27 12:47:47Z

2

function CheckTermsAcceptance(element){
    try{
       if (!element.checked){
            alert("You need to accept the terms by checking the box.")      
            return false;   
        }
    }catch(err){
        alert(err.description);
    }
}

and you call it like:

CheckTermsAcceptance(document.getElementById('chkStudent'));

is that it?

edited Oct 27, 2009 at 12:47

answered Oct 27, 2009 at 12:08

Victor

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1 Comment

John Feminella Over a year ago

This isn't really correct: the missing brace after the if statement will cause this to always return false. Submission of the form will be impossible.

gregers · Accepted Answer · 2009-10-27 12:07:50Z

0

Sorry for not answering your questions. But you should seriously consider using jQuery and jQuery validate.

answered Oct 27, 2009 at 12:07

gregers

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Comments

slyprid · Accepted Answer · 2009-10-27 12:20:59Z

You could also use more arguments to allow for different options as well.

function CheckTermsAcceptance()
{
    var ctrl = arguments[0];
    var valueExpected = arguments[1];
    var outputMessage = arguments[2];
    if(valueExpected == null) valueExpected = true;
    if(outputMessage == null) outputMessage = "You need to accept the terms by checking the box.";

    try
    {
        if(ctrl.checked == valueExpected)
        {
            Log.Message(outputMessage);
        }
    }
    catch(err)
    {
        alert(err.description);             
    }
}

barkmadley · Accepted Answer · 2009-10-27 12:34:51Z

this function will work with a bit of fix up, pass argument and make sure you do both the alert and the return false in the if statement

function CheckTermsAcceptance(checkBox) //added argument
{
    try
    {
        if (!checkBox.checked) { //added block to group alert and fail case
            alert("You need to accept the terms by checking the box.")      
            return false;
        }
        return true; //added success case
    }
    catch(err)
    {
        alert(err.description);
    }
}

once you have this in place you can then use it on your form validation like so

<form id="formid" action="" onsubmit="return validate('formid');">
<input type=checkbox name="name" id="name"><label for="name">Name</label>
<input type=checkbox name="name2" id="name2"><label for="name2">Name2</label>
<input type=submit>
</form>
<script>
function validate(formid) {
    var form = document.getElementById(formid);
    for (var i = 0; i < form.elements.length; i++) {
        var elem = form.elements[i];
        if (elem.type == 'checkbox' && !CheckTermsAcceptance(elem)) {
            return false;
        }
    }
    return true;
}
</script>

i can confirm that this works in firefox 3.5

also jQuery and jQuery.validate make this very easy to implement in a very declarative way.

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