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One of the essential skills in today’s e-commerce developer’s toolbox is JavaScript. JavaScript, originally developed by Netscape and released as LiveWire, has undergone a few transformations since its inception, even finding its way to the server side of e- commerce applications. Probably more often than not, however, it’s still used primarily on the client or, more specifically, with the browser. I’ll show you how to use it for one of the more common tasks in e-commerce development: form validation.

A Short History Lesson

JavaScript is a common term to most, but some may still be wondering how JScript or even ECMAScript fit in the scheme of things. By now, you should be painfully aware of the battles between Microsoft and Netscape. Everybody knows about the browser wars, but a lesser-known battle within that war is over scripting. Shortly after Netscape developed JavaScript, it was turned over to the European Computer Manufacturers Association (ECMA), an international standards organization. ECMA issued its standard, commonly known as ECMA-262, which has the title of ECMAScript language specification. Both JScript and JavaScript have arisen from this specification. ECMA-262 attempts to solve the matter of cross-browser compatibility, but this being the real world, there are obstacles to overcome. Microsoft’s standard practice of “extending” technologies means that JScript is ECMA-262-compliant and then some, adding a few more features here and there. Additionally, Netscape runs a little behind when it comes to keeping Navigator in pace with ECMA-262, although its JavaScript Version 1.3 claims full compliance.

JavaScript can reside in a source file external to the HTML page using the source, or it can be embedded directly into the HTML. When a JavaScript-enabled browser comes across a Web page that has JavaScript in it, the browser activates its scripting engine and begins to execute, or interpret, the JavaScript code. Without poring through the details of the ECMA standard, it’s hard to say which browser complies with the standard. Without going into too much detail about the ECMA-262 document (which can be downloaded at www.ecma.ch), I’ll leave it up to you to read the specification and see how it leaves the two scripting languages plenty of wiggle room, especially concerning the event model. Nevertheless, both scripting languages claim that they are in full compliance with ECMA- 262; however, there are still some instances where certain object properties and methods


work in either Navigator or Internet Explorer but not both. That is to say, cross-browser JavaScript is still the burden of the developer.

Fortunately, there is a way within JavaScript to detect the browser and version by which the developer will want to condition the processing of the script. For example, the following code snippet will detect your browser’s name and version. It works for all browsers despite using the navigator object.

var browser = navigator.appName;
var version = navigator.appVersion;

JavaScript for Client-side Validation

Among the many things you can use JavaScript for is to validate data that a user inputs into a form before that data gets sent across the wire to whatever you have waiting for it on the server. This use is probably the most common use of JavaScript in Web application programming. Your server-side component may be a Java servlet, an Active Server Page (ASP), or a CGI script. Whatever the component is, you don’t want it to choke, gasp, and wheeze by sending it data that it isn’t prepared to handle. JavaScript is an excellent choice to handle this task because all the validation is done on the client, i.e., the browser. Validation done through the browser gives far greater performance than having to send that form data to the server, having some sort of server-side data validation, and then having the server send back to the browser any errors that may have occurred. Sometimes this situation is unavoidable, and I’ll talk about that later.

There are several aspects to form validation, and I’ll cover them one-by-one. I’ll start out by discussing a little of what’s known as the event model. Every browser has its event model, which means that each browser has a way to let JavaScript know what event is taking place. For example, when a user presses a key on the keyboard, the onKeyPress event takes place, and if your JavaScript code does some processing on the onKeyPress event, it will be executed at that time. A major event for form validation is the onSubmit event, which is what normally kicks off form validation. The onSubmit event typically happens when a user presses an HTML button, created by the tag, that has Submit as the value for the tag’s Type parameter.

Common tasks involved with form validation are checking for missing values in required fields, checking the format of the data, providing the user with drop-down lists of valid data to enforce validity, or prompting the user for valid data á la the F4 key in OS/400.

Checking for missing values in required fields is relatively easy. Assuming a form called myForm was submitted as a form to be validated by a script, the way to check if FieldA contained any value at all is as follows:

if(myForm.FieldA.length == 0)

.. processing for missing data

Once a field that has data in it is passed to your validation script, you’ll probably want to make sure it’s in the format you want before handing it off to the server. The best example of this is validating dates. Of course, you’ll want to make sure that your dates are valid, that they’re in the correct month-day-year sequence, and that they have a valid date separator. That’s actually a lot to check for most developers, but since many of you have plenty of experience in RPG III, I’m sure you’re not scared to perform this basic but essential task.

Figure 1 is a simple HTML form with a collection of required fields to be validated. I’ve included a downloadable example of Figure 1 at www.midrangecomputing. com/mc. Look at the drop-down list of states. You’ll notice that the first value in the list is a text value: Select a state. By default, it is the value that is selected when the form first loads. You want to make sure that a user selects a value in the drop-down list other than the first


value, which is commonly a request to select a value, as in this example. To validate this field, you’ll use the following code:

var state = form.state.selectedIndex;
. . .

if (state == 0)

{

errors[count++] = “State error: ” +

“ Must select a state. ”;

}

The variable called form is the object that is passed to the validation script. A property of any form is a field name, in this case, State. Because State is a drop-down list created by the HTML tag