This chapter introduces server-side JavaScript and explains how it fits into the entire JavaScript language. It details what hardware and software you must have to use server-side JavaScript and how you must configure your web server to use server-side JavaScript.

Sections in this chapter:

• The JavaScript Language
• Architecture of JavaScript Applications
• System Requirements
• Configuration Information

Some aspects of the core language act differently when run on a server. In addition, to support the increased performance demands in these situations, JavaScript run on the server is compiled before installation, whereas the runtime engine compiles each client-side JavaScript script at runtime.

The components of JavaScript are illustrated in Figure 1.1.

Figure 1.1    The JavaScript language

Client-side JavaScript (or Navigator JavaScript) encompasses the core language plus extras such as the predefined objects only relevant to running JavaScript in a browser. Server-side JavaScript encompasses the same core language plus extras such as the predefined objects and functions only relevant to running JavaScript on a server. For a complete list of the differences, see "Server-Side Language Overview".

In this manual, the term JavaScript application refers to an application created using the full capabilities of JavaScript, that is, both client-side JavaScript and server-side JavaScript.

Client-side JavaScript is embedded directly in HTML pages and is interpreted by the browser completely at runtime. Because production applications frequently have greater performance demands upon them, JavaScript applications that take advantage of its server-side capabilities are compiled before they are deployed. The next two sections introduce you to the workings of JavaScript on the client and on the server.

Client-Side JavaScript

Figure 1.2    Client-side JavaScript

Client-side JavaScript statements embedded in an HTML page can respond to user events such as mouse clicks, form input, and page navigation. For example, you can write a JavaScript function to verify that users enter valid information into a form requesting a telephone number or zip code. Without any network transmission, the embedded JavaScript on the HTML page can check the entered data and display a dialog box if the user enters invalid data. For details on client-side JavaScript, see the JavaScript Guide.

Server-Side JavaScript

In contrast to pure client-side JavaScript scripts, HTML pages that use server-side JavaScript are compiled into bytecode executable files. These application executables are run in concert with a web server that contains the JavaScript runtime engine. For this reason, creating JavaScript applications is a two-stage process.

In the first stage, shown in Figure 1.3, you (the developer) create HTML pages (which can contain both client-side and server-side JavaScript statements) and JavaScript files. You then compile all of those files into a single executable.

Figure 1.3    Server-side JavaScript during development

In the second stage, shown in Figure 1.4, a client browser requests a page that was compiled into the application. The runtime engine finds the compiled representation of that page in the executable, runs any server-side JavaScript statements found on the page, and dynamically generates the HTML page to return. The result of executing server-side JavaScript statements might add new HTML or client-side JavaScript statements to the original HTML page. The runtime engine then sends the newly generated page over the network to the Navigator client, which runs any client-side JavaScript and displays the results.

Figure 1.4    Server-side JavaScript during runtime

In contrast to standard Common Gateway Interface (CGI) programs, all JavaScript source is integrated directly into HTML pages, facilitating rapid development and easy maintenance. JavaScript's Session Management Service contains objects you can use to maintain data that persists across client requests, multiple clients, and multiple applications. JavaScript's LiveWire Database Service provides objects for database access that serve as an interface to Structured Query Language (SQL) database servers. For more details on the server-side language, see Chapter 4, "Basics of Server-Side JavaScript."

Architecture of JavaScript Applications

Figure 1.5    Architecture of the client-server JavaScript application environment

The three tiers are:

• WWW clients (such as Netscape Navigator clients): This tier provides a cross-platform end-user interface to the application. This tier can also contain some application logic, such as data-validation rules implemented in client-side JavaScript. Clients can be inside or outside the corporate firewall.
• Netscape WWW server/database client: This tier consists of a Netscape server, with server-side JavaScript enabled. It contains the application logic, manages security, and controls access to the application by multiple users, using server-side JavaScript. This tier allows clients both inside and outside the firewall to access the application. The WWW server also acts as a client to any installed database servers.
• Database servers: This tier consists of SQL database servers, typically running on high-performance workstations. It contains all the database data, metadata, and referential integrity rules required by the application. This tier typically is inside the corporate firewall and can provide a layer of security in addition to that provided by the WWW server. Netscape Enterprise Server supports the use of ODBC, DB2, Informix, Oracle, and Sybase database servers. Netscape FastTrack Server supports only ODBC. For further information about the LiveWire Database Service, see Part 3, "LiveWire Database Service."

The top part of Figure 1.6 shows how server-side JavaScript fits into a Netscape web server. Inside the web server, the server-side JavaScript runtime environment is built from three main components which are listed below. The JavaScript Application Manager then runs on top of server-side JavaScript, as do the sample applications provided by Netscape (such as the videoapp application) and any applications you create.

Figure 1.6    Server-side JavaScript in the Netscape server environment

These are the three primary components of the JavaScript runtime environment:

• The JavaScript runtime library: This component provides basic JavaScript functionality. An example is the Session Management Service, which provides predefined objects to help manage your application and share information between the client and the server and between multiple applications. The Session Management Service is described in Chapter 5, "Session Management Service."
• The LiveWire database access library: This component extends the base server-side JavaScript functionality with classes and objects that provide seamless access to external database servers. It is described in Part 3, "LiveWire Database Service."
• The Java virtual machine: Unlike the other components, the Java virtual machine is not only for use with JavaScript; any Java application running on the server uses this virtual machine. The Java virtual machine has been augmented to allow JavaScript applications to access Java classes, using JavaScript's LiveConnect functionality. LiveConnect is described in Chapter 6, "Working with Java and CORBA Objects Through LiveConnect."

When you run a JavaScript application, a variety of things occur, some on the server and some on the client. Although the end user does not need to know the details, it is important for you, the application developer, to understand what happens "under the hood."

In creating your application, you write HTML pages that can contain both server-side and client-side JavaScript statements. In the source code HTML, client-side JavaScript is delimited by the SCRIPT tag and server-side JavaScript by the SERVER tag.

You can also write files that contain only JavaScript statements and no HTML tags. A JavaScript file can contain either client-side JavaScript or server-side JavaScript; a single file cannot contain both client-side and server-side objects or functions.

If the HTML and JavaScript files contain server-side JavaScript, you then compile them into a single JavaScript application executable file. The executable is called a web file and has the extension .web. The JavaScript application compiler turns the source code HTML into platform-independent bytecodes, parsing and compiling server-side JavaScript statements.

Finally, you deploy your application on your web server and use the JavaScript Application Manager to install and start the application, so that users can access your application.

At runtime, when a client requests a page from a server-side JavaScript application, the runtime engine locates the representation of that file in the application's web file. It runs all the server code found and creates an HTML page to send to the client. That page can contain both regular HTML tags and client-side JavaScript statements. All server code is run on the server, before the page goes to the client and before any of the HTML or client-side JavaScript is executed. Consequently, your server-side code cannot use any client-side objects, nor can your client-side code use any server-side objects.

For more details, see Chapter 4, "Basics of Server-Side JavaScript."

System Requirements

A JavaScript development environment consists of

• Development tools for authoring and compiling JavaScript applications. These tools typically are resident on the development machine.
• A development machine with a web server for running JavaScript applications that are under development.
• A deployment machine with a web server for deploying finished applications. End users access completed applications on this server.

• A JavaScript-enabled browser, such as Netscape Navigator, included in Netscape Communicator.
• A JavaScript application compiler, such as the one bundled with Netscape web servers.
• An editor, such as Emacs or Notepad.

• A web server.
• A JavaScript runtime engine, such as the one bundled with Netscape web servers.
• A way to configure your server to run JavaScript applications, as provided in the JavaScript Application Manager bundled with Netscape web servers.

• Relational database server software on your database server machine. For more information, refer to your database server documentation. In some cases, you may want to install the web server and the database server on the same machine. For specific requirements for server-side JavaScript, see Chapter 10, "Configuring Your Database."
• Your database's client and networking software on your web server machine. If you use one machine as both your database server and web server, typically the necessary database client software is installed when the database server is installed. Otherwise, you must ensure that the database client software is installed on the same machine as the web server, so that it can access the database as a client. For more information on database client software requirements, refer to the database vendor's documentation.

Enabling Server-Side JavaScript

NOTE: If you do not enable the JavaScript runtime engine, JavaScript applications cannot run on the server.

Protecting the Application Manager

You (the JavaScript application developer) need to have permission to use the Application Manager on your development server, because you use it to work with the application as you develop it. Your web server administrator, however, may choose to not give you this access to the deployment server.

When you enable the JavaScript runtime engine in the Server Manager, a prompt asks you whether to restrict access to the Application Manager. Choose Yes to do so, then click OK. (Yes is the default.) After this point, anyone attempting to access the Application Manager must enter the Server Manager user name and password to use the Application Manager and the dbadmin sample application. For more information, see the administrator's guide for your web server.

If your server is not using the Secure Sockets Layer (SSL), the user name and password for the Application Manager are transmitted unencrypted over the network. An intruder who intercepts this data can get access to the Application Manager. If you use the same password for your administration server, the intruder will also have control of your server. Therefore, it is recommended that you do not use the Application Manager outside your firewall unless you use SSL. For instructions on how to turn on SSL for your server, see the administrator's guide for your web server.

Setting Up for LiveConnect

You must either install your Java classes in this same directory or modify the CLASSPATH environment variable of the server to include the location of your Java classes. In addition, the CLASSPATH environment variable of the process in which you compile the Java classes associated with your JavaScript application must also include the location of your Java classes.

Remember, if you use the Admin Server to start your web server, you'll have to set CLASSPATH before you start the Admin Server. Alternatively, you can directly modify the obj.conf file for your web server. For information on this file, see your web server's administrator's guide.

On NT, if you modify CLASSPATH and you start the server using the Services panel of the control panel, you must reboot your machine after you set CLASSPATH in the System panel of the control panel.

Locating the Compiler

On Unix systems, you have various choices on how to change your PATH environment variable. You can add $NSHOME/bin/https, where $NSHOME is the directory in which you installed the server. See your system administrator for information on how to do so.

To change your NT system path, start the Control Panel application, locate the System dialog box, and set the PATH variable in the Environment settings to include the %NSHOME%\bin\https, where NSHOME is the directory in which you installed the server.

If you move the JavaScript application compiler to a different directory, you must add that directory to your PATH environment variable.

Last Updated: 10/30/97 12:18:19