[JavaScript]：如何将变量定义为对象类型？

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);
    }
}   

Answer 1

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.

Answer 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?

Answer 3

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

Answer 4

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.

Answer 5

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);             
    }
}