Client Side Vs. Server Side Code

In my experience, one of the most common pitfalls for beginning programmers is not understanding the relationships between objects in their environment. This is especially the case in web development where there is in almost every case a blend between multiple client side and server side scripts. Failure to understand the the way browsers and servers communicate or the relationships between (X)HTML (or JavaScript or CSS etc) and PHP (insert alternative language here) will certainly lead to a poor or incorrect implementation. If you are an experienced programmer you probably won’t gain much from reading this, but if you are a beginner, hopefully I can provide some insight that will save you a lot of trouble.

The difference between client side and server side code is fairly simple. Client side code is processed by the client (the browser to be more specific) while server side code is processed by the server. HTML for example is parsed by the browser; the browser is responsible for taking that code and turning it into what you see in your window. For the purposes of parsing web pages, there is a short list of the types of code the browser can deal with. A typical web page, as far as the client is concerned, consists of some flavor of HTML often supplemented by CSS, or JavaScript (an exhaustive list of the types of client side code is beyond the scope of this entry).

Server side code, on the other hand, is never seen by the browser. The browser is not and should never need to be aware of server side scripts such as PHP. While a web page consists of client side code, this code is often either partially or entirely generated by a server side script. For example:

$title = 'Client Side Vs. Server Side Code';
if($title == '')
	echo '<title>Tinsology</title>';
	echo "<title>$title</title>";

When you navigate to a page containing the code above the browser will see “<title>Client Side Vs. Server Side Code</title>”. That’s it. The browser does not see any of the PHP code that generated the title. When you request a page containing PHP code from the server, the server first processes that page and then sends the resulting output to the client.

Server side code is browser independent (unless explicitly coded otherwise). This means that if the page you create looks different in Internet Explorer than it does in Opera it has nothing to do with your PHP code, but rather the resulting client side code.

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