Client-Side vs Server-Side Scripting

Where does the code run?

	Client-side (JavaScript)	Server-side (PHP)
Runs on	The visitor's browser	Your web server
User can see source	Yes — View Source	No — only the HTML output
Access to DB	No (must go via API)	Yes — direct MySQL/Postgres
Access to files	No (sandboxed)	Yes — read/write any file the server can
Reacts to user input	Instantly (no network)	Needs a request to the server
Examples	clicks, form validation, animations	login, save to DB, send email, generate PDFs

Why both exist

Modern websites mix the two: PHP handles the "what" (data, auth, DB) while JavaScript handles the "how it feels" (clicks, animations, fetch). You can't replace PHP with JavaScript when you need a database or secret API key — the user could read them.

text
Browser  ←—HTML/CSS/JS——  Server (PHP)  ←—SQL——  Database
                            ↑
                       secret keys
                       business logic
                       user passwords

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