Chapter 6 Writing DynaScripts

Overview of scripts

You can embed scripts in HTML templates to control the information that the template provides to the user. The PowerDynamo script language, DynaScript, uses a syntax much like JavaScript. DynaScripts are interpreted by the application server, and the results of that interpretation are passed on to the Web server.

DynaScript has the following characteristics:

Scripts are usually embedded in an HTML template. You can also maintain a script as a separate file in the site, and include it in other scripts or templates, allowing for code reuse throughout the site.
Because DynaScript is processed at the application server, before the content is passed back to the client, no client support for scripting is required .
Script statements and variables are case-sensitive.
You do not need to declare variables.
Scripts can use the following datatypes:
- numeric
- logical (Boolean) true or false
- string
- null
- function
- object (methods and properties)
Variables do not have a fixed datatype. Datatype assignment occurs as needed when expressions are evaluated.
Control statements such as if , while , do-while and for have a syntax similar to C and Java.
You can create objects and define their properties and methods.
DynaScript includes several built-in object types for working with databases, SQL, and HTML documents.

Using a server-side language

Scripting languages for the Internet are interpreted at either the Web client or the Web server.

DynaScript is a server-side language that follows the ECMAScript standard (the standardized version of JavaScript). DynaScript has a syntax much like JavaScript. There are many uses for a server-side scripting language:

Maintaining information through a series of client accesses.
Detailed control over formatting of SQL queries.
Error-checking for SQL statements. For example, you can use scripts to check the success or failure of a delete statement, and to send an appropriate message to the Web client.
Client-independent form validation. It is quicker to validate entries in an HTML form at the Web client, but validation at the server makes an HTML form client-independent.
Server-side scripts can reduce the amount of data being sent to the client.

There are some tasks that can be better performed (or only performed) at the client side. For example, you cannot direct HTML to different frames in a window from the server side.

Why a JavaScript-based language?

There are several languages commonly used for Web-related tasks, including Java, JavaScript, and Perl. An ECMAScript compatible language provides several advantages in PowerDynamo:

While the strict typing and mandatory variable declaration of Java are desirable for large-scale application development, they can cause unnecessary overhead when developing small scripts attached to a single Web page.
The object-based structure of ECMAScript allows more readable and maintainable code than languages with many special features, such as Perl.

Implementing scripts

You can implement DynaScript in several ways:

You can embed scripts in HTML templates. This is the most straightforward way of using scripts, and how most of the examples in this chapter are presented.
You can write a script that generates an entire document (complete with HTML tags and queries). The Web client can request the script itself (rather than a separate HTML document), and the application server interprets the script to generate both the HTML and the query output to return to the client.
You can group common functions or class definitions into a separate script. You can then import this script into any other script or template that requires those functions or classes.