Server and client side processing

1.3.4 Web Technologies

Web Technologies — Note 4 of 4

Candidates need to understand the difference between server and client side processing, and should be aware of examples (for example Javascript code vs PHP code) of processing on both sides. Candidates should be aware of the benefits and drawbacks of both types of processing.

What you need to know

Processing for a web application can happen on the client (in the user's browser) or on the server. Each approach has benefits and drawbacks, and most websites use both.

What to know

Client-side benefits: reduces load on the server; quicker response because no round trip to the server is needed (e.g. instant form validation); reduces network traffic.
Client-side drawbacks: the code is visible and can be changed or disabled by the user, so it cannot be trusted for security; depends on the browser supporting it.
Server-side benefits: code is hidden from the user; more secure; can access databases and server resources; works regardless of the user's browser.
Server-side drawbacks: increases load on the server; each request needs a round trip, so it can be slower.
Example: validating that a form field is filled in can be done client-side for speed, but must be repeated server-side for security, e.g. checking login details against a database.

Key terms

Client-side processing: Code (usually JavaScript) is downloaded and run in the user's web browser.
Server-side processing: Code (e.g. PHP, Python) runs on the web server, and the results are sent back to the browser.

Exam technique

Tip:Any check that matters for security must be done server-side, because client-side code can be bypassed.

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