I was given a problem yesterday where I needed to do the following client-side validation. If a user selects a checkbox that they wish to enable credit card transactions, I need to display a panel of specific credit card companies and they need to select at least one before submitting.

If you think about writing the JS to do this without a library it is a somewhat lengthy task. In essence, you would need to do some type of an onsubmit function on your form, check the value of the key checkbox. If it was checked, check the value of each credit card checkbox to see if the user had selected one of the children. After writing this in JQuery, I thought it might be worth demonstrating what an easy task this is.

Let's start with the specific part of my form that has my checkboxes:

<label for="RequireCCInfo">Require Credit Card Information?</label>
<input name="RequireCCInfo" id="RequireCCInfo" value="1" type="checkbox">
<div id="CreditCardCompanyPanel">
	<div>
		<input id="ccAmex" class="ccCheckBox" value="1" type="checkbox">
		<label for="ccAmex">American Express</label>
	</div>
	<div>
		<input id="ccVisa" class="ccCheckBox" value="1" type="checkbox">
		<label for="ccVisa">Visa</label>
	</div>
	<div>
		<input id="ccDiscover" class="ccCheckBox" value="1" type="checkbox">
		<label for="ccDiscover">Discover</label>
	</div>
	<div>
		<input id="ccMc" class="ccCheckBox" value="1" type="checkbox">
		<label for="ccMc">Master Card</label>						
	</div>
</div>

There is nothing too notable in all of that other than the fact that you should notice that I have added a class "ccCheckBox" to all of my dependent checkboxes. I will explain more on that in a bit, but I wanted to point out that it is there. You will also notice that I am not doing anything in the way of hiding the "CreditCardCompanyPanel" div. We need to determine at request time whether that will be hidden or not based on whether the "RequireCCInfo" checkbox is checked.

Now, here is the fun part... I am including the JS that I use for this task below:

<script language="javascript">	
(document).ready(function(){
	$("#RequireCCInfo").change(function(){
		toggleCreditCardCompanyPanel();
	}); 	
	function toggleCreditCardCompanyPanel()	{
		if ($("#RequireCCInfo").attr("checked") == true) 	$("#CreditCardCompanyPanel").show();	
		else $("#CreditCardCompanyPanel").hide();
	}
	$("#SaveButton").click(function(){
		var pass = false;
		if ($("#RequireCCInfo").attr("checked") == true){
			$(".ccCheckBox").each(function() {
               			if ($(this).attr("checked") == true) pass = true;
            		});
		}
		else pass = true;
		if (pass) $("#frmMyForm").submit();
		else alert('You must select at least on credit card company if "Require Credit Card Information" is checked.');
	}); 
	toggleCreditCardCompanyPanel();
});
</script>

First, by using the $(document).ready() function we are telling JQuery to run this JS once the DOM has been completely loaded. Let's look at each section within that ready() block...

The first thing you will see is the $("#RequireCCInfo").change() method. JQuery gives us the concept of binding a listener to an element. For our example, this listener says that anytime that an element with an ID of "RequireCCInfo" is changed, that we will run the code in its function(). You will see that anytime our "RequireCCInfo" checkbox is changed we are going to run a function called toggleCreditCardCompanyPanel(). As you can see we have that method defined immediately after our "RequireCCInfo" checkbox.

In our toggleCreditCardCompanyPanel() method, we are making the decision as to whether or not our "CreditCardCompanyPanel" will be displayed based on whether our user has decided to check the box labeled "Require Credit Card Information?". By using the JQuery selectors we are in essence saying: If a checkbox with an ID of "RequireCCInfo" is checked, display an element with the ID "CreditCardCompanyPanel". Otherwise we will hide this element.

Next comes our validation on form submit... and pretty cool stuff!

Basically I have added a listener which is bound to our submit button with the ID of "SaveButton" which will submit our form "frmMyForm". Anytime that this button is clicked, we will run the code in the function() block. We start this function by setting a value pass=false. We will use this variable to determine whether our form has passed validation. Next we get just a small taste of the magic of JQuery selectors. First, as we did in the toggleCreditCardCompanyPanel() function, we are determining if the element with the ID of "RequireCCInfo" is checked. If so, by using the each() function, we are going to loop through all elements on the page with the class "ccCheckBox" (remember that from above?). In each iteration of the loop we are going to determine if the element has been checked. If so, we are going to set pass=true since we know that our validation has passed.

Lastly, now that we have determined that our form is either going to pass/fail, we take the appropriate action. If pass==fail, we are simply going to alert a message telling the user that if they are going to enable credit cards that they have to choose at least one credit card company. Otherwise, we are going to call the submit() method on our form.

I almost took the time to write out the equivalent of this in POJS (plain old JavaScript) to show how much easier life is with JQuery, but I realized I didn't have the time, patience, or will. JQuery has spoiled me!