I receive an excessive number of questions asking for help and asking how to do certain coding tasks. One question this week caught me by surprise. In a prior article, I presented a method for separating the scripting code form your actual HTML file. This raised the question about running the javascript on the server rather than on the client so that the client could not see the code. This question raised a critical issue for understanding Web programs to understand the different types of Web applications that can be created, you should understand the difference between client-side and server-side code.
Web pages are displayed in your browser on your local machine. Just like a customer or client for a restaurant, you and your browser are a client using a Web site. The Web site is displayed by your browser, which interprets code that was sent to it. In general this code will be primarily HTML, but may also contain anything supported by your browser such as javascript, flash movies, and more.
The machine where the Web site actually resides is called a Web server. When you send a request for a Web page by entering a Web site address, this request is sent to a Web Server. The Web server then sends the Web page to your browser. The interesting thing about a Web server is that it can manipulate the code within a Web page before sending it to your browser. For most Web pages, no manipulation is done. Rather, the server simply sends a copy to the browser and the browser does the work of displaying the code.
A Web Server can manipulate what is included in a Web page before sending it. When the request is made to a server to send a Web page, the server can actually execute a program instead. This can be a program written in a variety of languages. Some of the programming languages and technologies that can be used are Active Server Pages (ASP), PHP, C/C++, and ISAPI, Java Server Pages (JSP), and more. Of course, in order to use any of these languages, the server must support them.
An important issue when working with Web applications is to remember that the Web server is separate from the Web browsers that will use a Web site’s pages. The Web server can be located anywhere in the world — or even off the world! The browser is generally on a machine you are using. Stated a different way, you can act as a customer, or client, using a browser to access a Web site that is located on a Web server.
The programs running on the Web Server are server side programs because they are on the side of the internet that the Web server is on. The browser being used to access the Web site is on the same side of the Web as you, the client side. If code is executed on the Web server, it is considered server side code. If code is executed on your browser, it is considered client-side. Because the internet is vast, the client side and server side programs are not constantly in contact with each other. Because of this, there is code that you can use on the server and there is code that you can use on the client.
What do you do on the server?
There are a number of types of programming things that can be done on the server. One of the primary functions you can do with code is to prepare the code that is to be sent to the Web browser. This includes such tasks as building pages customized for the type of browser that requested a page. It could also include doing tapping into a database to create information for a Web page. A very popular server side program is a Visitor Counter that keeps track of the number of people who have accessed a Web Site. The counter program would keep track of people who have come and store the information. It would also provide the actual number for any Web pages that are sent back to a browser.
What do you do on the client?
HTML, javascript, Flash files, ActiveX controls, Java applets, and a number of other technologies can be executed on the client side. You can execute any technology supported by your browser. Client side programming is used because the browser is separate from the server. By including code within a web page, a number of features can be added to a Web page without the need to send information to the Web Server which takes time. Tasks done on the client side include data validation, special formatting features that go beyond HTML, controls that take care of page navigation and ad presentation, and more.
In Summary…
In summary, when developing applications for the Web you need to understand the differences between what is happening on the server side and what is happening on the client side. By understanding the difference, you will be able to build Web sites that are more efficient.
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