// server-side programming

What Is PHP?

PHP is a programming language widely used for server-side web development. It can generate web pages, process forms, communicate with databases, manage sessions and build dynamic websites and applications.

// definition

PHP is a server-side scripting language

PHP is a general-purpose programming language particularly suited to web development.

PHP code commonly runs on a web server rather than directly inside the user's browser.

The server executes the PHP code and sends the resulting output, often HTML, back to the browser.

// name

What does PHP stand for?

PHP is officially described using the recursive acronym:

PHP: Hypertext Preprocessor

The name reflects PHP's long association with generating and processing web content.

// example

What does PHP look like?

<?php echo "Hello, world!"; ?>

The echo statement sends text to the output.

In a web application, that output can become part of the HTML returned to the browser.

// server

PHP usually runs before the page reaches the browser

Browser requests page ↓ Web server receives request ↓ PHP code executes ↓ PHP generates output ↓ Server sends response ↓ Browser displays page

The browser usually receives the output generated by PHP rather than the original PHP source code.

// php + html

PHP can be embedded inside HTML

<h1>Welcome</h1> <p> Today is <?php echo date("d F Y"); ?> </p>

PHP executes on the server and inserts the generated value into the document before it is sent to the user.

// variables

PHP can store information in variables

<?php $name = "Alice"; $orders = 4; echo $name; echo $orders; ?>

PHP variable names normally begin with a $ symbol.

// data types

PHP supports different kinds of data

Type	Example
String	"Freelance Coder"
Integer	42
Float	19.99
Boolean	true
Array	["HTML", "CSS", "PHP"]
Null	null
Object	new Customer()

// arrays

PHP arrays can store collections of data

<?php $skills = [ "HTML", "CSS", "JavaScript", "PHP" ]; echo $skills[0]; ?>

This outputs:

HTML

// associative arrays

PHP arrays can also use named keys

<?php $customer = [ "name" => "Alice", "orders" => 4, "active" => true ]; echo $customer["name"]; ?>

Associative arrays are useful for representing structured information using named keys and values.

// conditions

PHP can make decisions

<?php $loggedIn = true; if ($loggedIn) { echo "Welcome back."; } else { echo "Please sign in."; } ?>

Conditional statements allow different code to run depending on the state of the application.

// functions

PHP functions package reusable logic

<?php function greet($name) { return "Hello, " . $name; } echo greet("Alice"); ?>

The full stop operator joins strings together in PHP.

// loops

PHP can repeat tasks

<?php for ($i = 1; $i <= 5; $i++) { echo $i; } ?>

Loops are useful when the same operation must be repeated several times.

// foreach

foreach is useful for collections

<?php $skills = [ "HTML", "CSS", "PHP" ]; foreach ($skills as $skill) { echo $skill; } ?>

The loop processes each item in the array one at a time.

// forms

PHP can process form submissions

A website might contain a form:

<form method="post"> <input type="text" name="name" > <button type="submit"> Send </button> </form>

PHP can receive the submitted data:

<?php if ($_SERVER["REQUEST_METHOD"] === "POST") { $name = $_POST["name"] ?? ""; } ?>

User input should be validated and handled safely. Real applications should never assume that submitted information is automatically trustworthy.

// databases

PHP can communicate with databases

PHP is commonly used with relational databases such as MySQL and PostgreSQL.

An application might use a database to store:

Users Products Orders Blog Posts Settings Transactions

// database connection

PHP provides database interfaces

One common approach is PHP Data Objects, or PDO.

<?php $pdo = new PDO( "mysql:host=localhost;dbname=shop;charset=utf8mb4", $username, $password ); ?>

Applications can then execute database queries through the connection.

// sql safety

Prepared statements are important

<?php $stmt = $pdo->prepare( "SELECT * FROM users WHERE email = ?" ); $stmt->execute([$email]); $user = $stmt->fetch(); ?>

Prepared statements allow values to be supplied separately from the SQL structure and are an important defence against SQL injection.

// sessions

PHP can maintain session data

<?php session_start(); $_SESSION["user_id"] = 123; ?>

Sessions allow a server to associate information with a user across multiple requests.

They are commonly used for login systems and other stateful website features.

// cookies

PHP can also work with cookies

<?php setcookie( "theme", "light", time() + 3600 ); ?>

Cookies are stored by the browser and can later be sent back to the server with requests.

// json

PHP works with JSON

PHP can convert arrays and objects into JSON:

<?php $data = [ "name" => "Alice", "orders" => 4 ]; echo json_encode($data); ?>

It can also convert JSON into PHP data:

<?php $data = json_decode( $json, true ); ?>

This makes PHP useful for building and consuming APIs.

// APIs

PHP can power APIs

Instead of returning an HTML page, a PHP application can return structured data.

<?php header( "Content-Type: application/json" ); echo json_encode([ "status" => "success", "message" => "Data received" ]); ?>

Another application can then consume the JSON response.

// php vs javascript

PHP and JavaScript often work together

PHP

Commonly runs on the server and handles server-side application logic.

JavaScript

Commonly runs in the browser and handles interactive client-side behaviour.

PHP Output

Can generate HTML or JSON that is sent to the browser.

JavaScript Requests

Can send requests to PHP-powered APIs and process their responses.

// web application

A PHP web application might work like this

User ↓ Browser ↓ HTTP request ↓ Web server ↓ PHP application ↓ Database ↓ PHP generates response ↓ HTML or JSON ↓ Browser

PHP often acts as the server-side layer connecting users, application logic and stored data.

// wordpress

WordPress is built with PHP

PHP has played a major role in the development of content management systems.

WordPress uses PHP extensively for themes, plugins, templates, database interaction and server-side logic.

<?php the_title(); the_content(); ?>

WordPress-specific PHP functions can dynamically retrieve and display website content.

// .php files

PHP code is commonly stored in .php files

index.php contact.php login.php api.php functions.php

A web server configured for PHP can execute the PHP code when one of these files is requested.

// security

Server-side code must handle data carefully

PHP applications often process passwords, form inputs, database queries, cookies and uploaded files.

Secure applications therefore need appropriate validation, escaping, authentication and database practices.

Never trust input simply because it came from your own website. Server-side code should validate data and apply the correct security controls for how that data will be used.

// frameworks

PHP has a large software ecosystem

Developers can use frameworks and content management systems rather than building every component from scratch.

Laravel Symfony WordPress Composer PHPUnit

// uses

What is PHP used for?

Dynamic Websites WordPress APIs Databases Forms Authentication E-commerce Web Applications Server-Side Logic Automation

// summary

The server does the work.

PHP is a programming language widely used for server-side web development. It can generate HTML, process forms, manage sessions, communicate with databases, work with JSON and APIs, and power dynamic websites and applications such as WordPress.

// programming

What Is JavaScript?

JavaScript is a programming language used extensively on the web. It allows websites to respond to users, manipulate page content, communicate with servers, process data and perform tasks dynamically.

// definition

JavaScript adds logic and behaviour

JavaScript is a high-level programming language used in web browsers, servers and many other software environments.

On a web page, JavaScript can react to user actions, change HTML content, modify CSS styles, process data and communicate with APIs.

It is one of the core technologies of modern web development alongside HTML and CSS.

// example

What does JavaScript look like?

A very simple JavaScript statement might be:

console.log("Hello, world!");

This tells JavaScript to send the text Hello, world! to the developer console.

// variables

JavaScript can store information

Variables allow programs to store values for later use.

let name = "Alice"; let orders = 4; console.log(name); console.log(orders);

Here, one variable stores text and another stores a number.

// let + const

Values can be declared with let and const

let score = 10; score = 20; const siteName = "Freelance Coder";

let is commonly used when a variable may later be assigned another value.

const creates a binding that cannot later be reassigned.

// data types

JavaScript works with different kinds of data

Type	Example
String	"Freelance Coder"
Number	42
Boolean	true
Undefined	undefined
Null	null
Object	{ name: "Alice" }
BigInt	123n
Symbol	Symbol("id")

// arrays

Arrays store collections of values

const skills = [ "HTML", "CSS", "JavaScript", "PHP" ];

Individual values can be accessed by their position.

console.log(skills[0]);

This produces:

HTML

JavaScript array indexes begin at 0. The first item therefore has index 0 rather than 1.

// objects

Objects group related information

const customer = { name: "Alice", orders: 4, active: true };

The object's properties can then be accessed:

console.log(customer.name);

This produces:

Alice

// operators

JavaScript can perform calculations

let a = 10; let b = 5; let total = a + b; console.log(total);

The result is:

15

+ - * / % **

// conditions

Programs can make decisions

Conditional statements allow code to behave differently depending on whether a condition is true or false.

const loggedIn = true; if (loggedIn) { console.log("Welcome back."); } else { console.log("Please sign in."); }

// functions

Functions package reusable behaviour

function greet(name) { return "Hello, " + name; } console.log(greet("Alice"));

The function receives a value, performs some logic and returns a result.

This makes code easier to organise and reuse.

// arrow functions

JavaScript also has arrow functions

const add = (a, b) => { return a + b; }; console.log(add(3, 4));

This outputs:

7

// loops

JavaScript can repeat tasks

for (let i = 1; i <= 5; i++) { console.log(i); }

This repeats the same instruction while the loop condition remains true.

// dom

JavaScript can change a web page

In a browser, JavaScript can interact with the Document Object Model, usually called the DOM.

Suppose the HTML contains:

<h1 id="title">Old Title</h1>

JavaScript could change it:

document.getElementById("title").textContent = "New Title";

The visible heading can change without loading an entirely new HTML document.

// events

JavaScript can respond to users

Browsers generate events when users click buttons, type into forms, move the mouse and perform other actions.

const button = document.getElementById("button"); button.addEventListener("click", function () { alert("Button clicked!"); });

JavaScript waits for the click event and then runs the function.

// html + css + javascript

The three core web technologies have different roles

HTML

Defines the structure and meaning of the page.

CSS

Controls presentation, layout and visual design.

JavaScript

Adds logic, behaviour and interactivity.

Together

They form the foundation of much of modern front-end web development.

// example

HTML, CSS and JavaScript working together

HTML:

<button id="helloButton"> Say Hello </button>

CSS:

#helloButton { background: #001eff; color: white; padding: 12px 18px; }

JavaScript:

document .getElementById("helloButton") .addEventListener("click", function () { alert("Hello!"); });

HTML creates the button, CSS styles it and JavaScript gives it behaviour.

// APIs

JavaScript can communicate with APIs

JavaScript can request data from another service over the web.

fetch("https://api.example.com/products") .then(response => response.json()) .then(data => { console.log(data); });

This example requests information from an API and converts the response into JavaScript data.

// javascript + json

JavaScript works naturally with JSON

JSON was derived from JavaScript object notation and is widely used to exchange structured information.

{ "name": "Alice", "orders": 4 }

JavaScript can parse JSON text:

const customer = JSON.parse(jsonText);

It can also convert JavaScript values into JSON:

const json = JSON.stringify(customer);

// asynchronous code

JavaScript can handle asynchronous tasks

Some operations take time, such as requesting information from a server.

JavaScript provides mechanisms such as promises and async/await for working with these tasks.

async function getData() { const response = await fetch("/api/data"); const data = await response.json(); console.log(data); }

// runtime

JavaScript is not limited to browsers

JavaScript originally became popular as a browser language, but it can now run in many other environments.

Web Browsers Servers Node.js Web Apps Desktop Apps Automation Cloud Functions

// node.js

Node.js allows JavaScript to run outside the browser

Node.js is a JavaScript runtime commonly used for server-side programming, command-line tools and automation.

console.log( "JavaScript running with Node.js" );

This means the same language can be used for both browser-based and server-side development.

// javascript vs java

JavaScript is not Java

JavaScript and Java are different programming languages. Despite the similarity in their names, they have different histories, syntax, ecosystems and execution models.

// dynamic typing

JavaScript is dynamically typed

A variable can hold values of different types at different times.

let value = 10; value = "Hello"; value = true;

The variable itself is not permanently restricted to one of these types.

// modules

JavaScript code can be divided into modules

Larger applications can separate functionality into reusable files.

export function add(a, b) { return a + b; }

Another JavaScript file can import that function:

import { add } from "./math.js"; console.log(add(2, 3));

// uses

What is JavaScript used for?

Interactive Websites Web Applications APIs Data Processing Automation Servers Forms Animations AI Interfaces Browser Tools

// summary

Structure and design become interactive.

JavaScript is a programming language used to add logic, behaviour and interactivity to websites and applications. It can manipulate HTML, change CSS, process data, respond to users, communicate with APIs and run on both browsers and servers.