This is a sample chapter from Professional Javascript.

In this chapter you will learn how to:

• Build dynamic pages using server-side JScript v5 and ADO 2.1 to pull information from a SQL Server 7 database
• Validate form based user input using client-side JavaScript
• Persist state from page to page using cookies
• Harness Active Server Page's transaction support via MTS (Microsoft Transaction Server) to process orders and store user orders in a database
• Send e-mails using Microsoft's CDONTS (Collaboration Data Objects for Windows NT Server)

To work through this example, you will need access to Windows NT Server 4 or Windows 2000 with SQL7.0, JScript v5.0, IIS4 or 5, MTS, a simple mail server and a text editor installed upon it. Note also that where we have split lines of code onto two or more lines for clarity's sake, this has been marked with an underscore.

MusicMadOnline.com

Our imaginary client MusicMadOnline.com sells music compact discs and wants an online store to sell their products. They want customers to be able to browse their electronic shelves based on music genre. However they don't want their product lists or the categories to be hardwired in to the HTML pages although they do require the addition of new products and categories to be reflected automatically in the HTML pages.

Once the customer has selected their goods they must then be able to place an order online using a credit card for payment. Once an order has been accepted, the shipping department must be notified by e-mail of the customer's delivery address and items to be sent. The customer must also be notified by e-mail that their order has been accepted and will be delivered shortly.

Design aims

Businesses want to make money and can't afford to turn away customers. It's for this reason that the client-side part of MusicMadOnline.com has been designed to work on Internet Explorer and Netscape Navigator browsers version 3 and above. If we want to include Dynamic HTML effects particular to say IE4 or 5 then separate pages would most likely have to be written. Although it is possible to include support for different browsers in the same page, things can quickly get confusing.

On the server-side we have control of what version of JavaScript we use. Here I have used features available in JavaScript 1.2 and in particular those available in Microsoft's JScript Version 5.0 which comes with Internet Explorer 5.0 (IE5). If you don't want to install IE5 on your server than you can download the version 5.0 scripting engine from the Microsoft site (http://msdn.microsoft.com/scripting/jscript/default.htm) and install it on your server. Perhaps the best reason for upgrading to JScript v5 is its support of exception handling using the try…catch statement, but more on this later.

In anticipation of our online store being hugely popular we need to ensure it can cope with large numbers concurrent users and database transactions. It may be tempting to use something like Microsoft Access as our back end database, but as even Microsoft admit, Access won't cut it for high numbers of concurrent users. Instead I have used SQL Server 7 as the back-end database, though there are plenty of other high-end databases available which can provide the power we need.

SQL Server 7 also provides a greater level of sophistication, such as compiled stored procedures, which by modularizing our database code will make it more maintainable and as a bonus achieve greater scalability through being pre-compiled.

When dealing with large databases ensuring they don't become corrupted is always important. By this I mean that we don't want the situation where halfway through processing a customer's order we hit an unexpected error causing our application to drop out leaving the database in an inconsistent state. Either a transaction completes fully and the customer gets their goods or it fails and is rolled back completely and the customer is informed of this fact and where possible given information on why it happened and how they can proceed to complete their order. To help us with this objective we will make use of support for Microsoft Transaction Server transactions in ASP.