// 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.

// web development

What Is CSS?

CSS is the language used to control the appearance and layout of web pages. HTML describes the structure of the content, while CSS determines how that content should look.

// definition

CSS means Cascading Style Sheets

CSS stands for Cascading Style Sheets.

It is a stylesheet language used to describe the presentation of HTML and other structured documents.

CSS can control colours, fonts, spacing, borders, positioning, page layout, animations and how a website adapts to different screen sizes.

// example

What does CSS look like?

Suppose a web page contains this HTML:

<h1>Freelance Coder</h1>

We could style that heading using CSS:

h1 { color: blue; font-size: 40px; text-align: center; }

The HTML identifies the content as a heading. The CSS controls how that heading is displayed.

// css rule

CSS is written as rules

p { color: #20262d; font-size: 18px; }

A CSS rule contains a selector and one or more declarations.

Selector

Identifies which HTML elements should receive the styling.

Declaration

Specifies the property that should change and the value it should receive.

// property + value

Properties and values control the design

color: blue;

In this declaration:

Part	Meaning
color	The CSS property
blue	The value assigned to the property

A colon separates the property from the value, and declarations normally end with a semicolon.

// selectors

CSS selectors choose what to style

CSS provides several ways to target HTML elements.

/* Every paragraph */ p { color: black; } /* Elements with class="button" */ .button { background: blue; } /* Element with id="header" */ #header { padding: 20px; }

Element Selector Class Selector ID Selector Attribute Selector Pseudo-class

// classes

Classes make styles reusable

An HTML element can be given a class:

<a class="button">Contact Me</a>

CSS can then target that class:

.button { background: #001eff; color: white; padding: 10px 18px; border-radius: 6px; }

The same class can be applied to multiple elements, allowing the styling to be reused.

// colours

CSS controls colour

Colours can be represented in several ways.

color: blue; color: #001eff; color: rgb(0, 30, 255); color: rgba(0, 30, 255, 0.5);

Your Freelance Coder site, for example, uses:

Normal link: #001eff Hover: #00d719 Visited link: #5b3fd6

// typography

CSS controls text appearance

p { font-family: Arial, sans-serif; font-size: 18px; font-weight: 400; line-height: 1.7; }

CSS can control the typeface, size, weight, spacing and alignment of text.

// box model

HTML elements are treated like boxes

One of the most important CSS concepts is the box model.

An element can have:

Content

The text, image or other content inside the element.

Padding

Space between the content and the border.

Border

A line surrounding the element and its padding.

Margin

Space outside the element separating it from surrounding elements.

.card { padding: 20px; border: 1px solid #e3e8ee; margin: 20px; }

// dimensions

CSS controls dimensions

.container { width: 100%; max-width: 720px; min-height: 300px; }

Widths and heights can be expressed using pixels, percentages, viewport units and other CSS units.

// flexbox

CSS can arrange elements with Flexbox

.container { display: flex; gap: 20px; align-items: center; justify-content: space-between; }

Flexbox is useful for arranging elements along a row or column and controlling their alignment and spacing.

// grid

CSS Grid can create page layouts

.services { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }

This creates two equal-width columns.

CSS Grid is particularly useful for layouts involving rows and columns.

// responsive design

CSS can adapt a website to different screens

Media queries allow styles to change depending on properties such as the width of the screen.

@media (max-width: 600px) { .services { grid-template-columns: 1fr; } }

A two-column desktop layout could therefore become a single-column layout on a phone.

// interaction

CSS can respond to user interaction

Pseudo-classes such as :hover can apply styles when a user interacts with an element.

a { color: #001eff; } a:hover { color: #00d719; }

This is the same basic idea behind the green hover effects used throughout Freelance Coder.

// transitions

CSS can create smooth transitions

a { color: #001eff; transition: color 0.25s ease; } a:hover { color: #00d719; }

Instead of the colour changing instantly, the browser transitions smoothly between the two colours.

// animation

CSS can also create animations

@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } } .card { animation: fadeIn 0.6s ease; }

CSS animations can change properties over time without requiring JavaScript for every visual effect.

// cascade

Why is it called "Cascading" Style Sheets?

More than one CSS rule can potentially apply to the same element.

The browser must therefore determine which declaration wins.

The result depends on factors including:

Origin Importance Specificity Scope Source Order

The cascade is a core part of CSS. It provides a defined system for resolving competing style declarations.

// inheritance

Some CSS properties are inherited

Certain properties can pass from a parent element to its descendants.

body { color: #20262d; font-family: Arial, sans-serif; }

Text inside many child elements may inherit these properties automatically unless another rule overrides them.

// adding css

CSS can be added in several ways

Method	Example
External stylesheet	styles.css
Internal stylesheet	<style> ... </style>
Inline style	style="color: blue;"

Larger websites usually benefit from reusable stylesheets rather than repeating styles directly inside individual HTML elements.

// external stylesheet

CSS can live in its own file

A stylesheet might be saved as:

styles.css

HTML can then load it using:

<link rel="stylesheet" href="styles.css" >

This separation allows one stylesheet to control the appearance of many pages.

// html + css + javascript

HTML, CSS and JavaScript have different roles

HTML

Defines the structure and meaning of the content.

CSS

Defines the presentation, design and layout.

JavaScript

Adds programming logic, behaviour and interactivity.

Together

They form the core technologies behind much of modern front-end web development.

// separation

Structure and presentation can be separated

HTML might contain:

<button class="contact-button"> Contact Me </button>

CSS can separately define how it looks:

.contact-button { background: #001eff; color: white; padding: 12px 18px; border: 0; border-radius: 8px; } .contact-button:hover { background: #00d719; }

The HTML describes the button. CSS controls its presentation.

// css vs html

CSS does not replace HTML

CSS normally styles an existing document structure.

Without HTML or another document language providing the content and structure, there is little for ordinary CSS to style.

HTML describes what the content is. CSS describes how that content should be presented.

// uses

What is CSS used for?

Colours Typography Layouts Spacing Responsive Design Hover Effects Animations Navigation Forms Web Design

// summary

Structure becomes design.

CSS is the stylesheet language used to control how web content is presented. It works alongside HTML to control colours, typography, spacing, dimensions, layouts, responsive behaviour, hover effects and animations, making it one of the fundamental technologies of the modern web.

// web development

What Is HTML?

HTML is the markup language used to describe the structure and meaning of content on web pages. It tells a web browser what elements exist on a page and how those elements relate to one another.

// definition

HTML means HyperText Markup Language

HTML stands for HyperText Markup Language.

It is the standard markup language used to structure content on the World Wide Web.

HTML can describe headings, paragraphs, links, images, lists, tables, forms and many other parts of a web page.

// example

What does HTML look like?

A very simple piece of HTML might look like this:

<h1>Freelance Coder</h1> <p>Welcome to my website.</p>

The browser interprets the first element as a main heading and the second as a paragraph.

// elements

HTML is built from elements

An HTML element usually consists of an opening tag, some content and a closing tag.

<p>This is a paragraph.</p>

<p>

The opening tag marks the beginning of the paragraph.

</p>

The closing tag marks the end of the paragraph.

// terminology

A tag and an element are not quite the same thing

People often use the words interchangeably, but there is a useful distinction.

<h2>About Me</h2>

<h2> is a tag.

The complete structure including the opening tag, content and closing tag is the HTML element.

// attributes

Elements can have attributes

Attributes provide additional information about an HTML element.

<a href="https://example.com">Visit Example</a>

The href attribute tells the browser where the link should go.

<img src="photo.jpg" alt="A photograph">

Here, src identifies the image file and alt provides alternative text.

// document

A complete HTML document has a structure

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Freelance Coder</title> </head> <body> <h1>Hello, world!</h1> <p>This is my web page.</p> </body> </html>

// head

The <head> contains information about the page

The head normally contains metadata and resources used by the document rather than the main visible page content.

Page Title Character Encoding Metadata Stylesheets Scripts

// body

The <body> contains the page content

Most of the content that users see and interact with appears inside the body element.

<body> <h1>My Website</h1> <p>Welcome to my website.</p> <a href="/contact">Contact me</a> </body>

// common elements

Some common HTML elements

Element	Purpose
<h1>	Main heading
<p>	Paragraph
<a>	Link
<img>	Image
<ul>	Unordered list
<ol>	Ordered list
<table>	Tabular data
<form>	User input form

// hypertext

HTML links pages together

The "HyperText" part of HTML refers to the ability to connect documents through hyperlinks.

<a href="https://example.com">Open website</a>

Links are one of the fundamental ideas behind the web. They allow users to move between pages, websites and other resources.

// nesting

HTML elements can contain other elements

<article> <h2>What Is HTML?</h2> <p> HTML structures web content. </p> </article>

This creates a hierarchical document structure.

The article contains both a heading and a paragraph.

// semantic html

HTML can describe meaning, not just appearance

Modern HTML includes semantic elements that describe the purpose of different sections of a page.

<header> <nav> <main> <article> <section> <footer>

Semantic HTML can make documents easier for browsers, developers, search engines and assistive technologies to understand.

// html + css + javascript

HTML, CSS and JavaScript have different jobs

HTML

Defines the structure and meaning of the content.

CSS

Controls presentation, layout, colours, spacing and visual design.

JavaScript

Adds behaviour, logic and interactive functionality.

Together

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

// structure vs style

HTML describes what something is

Consider:

<h1>Freelance Coder</h1>

HTML tells the browser that this text is the main heading.

CSS could then decide that the heading should be blue, large and centred.

h1 { color: blue; font-size: 42px; text-align: center; }

Keeping structure and presentation separate is an important principle of web development.

// markup language

HTML is a markup language

HTML is generally described as a markup language, rather than a programming language.

Its main purpose is to mark up and describe the structure and meaning of document content.

HTML structures content. It does not by itself provide the general-purpose programming logic associated with languages such as JavaScript, Python or PHP.

// utf-8

HTML and UTF-8

HTML is text, so character encoding matters.

Modern pages commonly declare UTF-8 using:

<meta charset="UTF-8">

This helps browsers correctly interpret characters such as:

£ € é π √ ≤ ≥ 日

// browser

The browser interprets the HTML

When a browser receives an HTML document, it parses the markup and constructs an internal representation of the page.

HTML file ↓ Browser parses HTML ↓ Document structure ↓ CSS applied ↓ JavaScript can interact with the page ↓ Rendered web page

The browser does not simply display the HTML source code. It interprets the markup and renders the corresponding document.

// accessibility

Good HTML also improves accessibility

Correctly structured HTML gives information about headings, navigation, images, forms and other content.

Assistive technologies such as screen readers can use this structure to help users understand and navigate a page.

<img src="chart.png" alt="Bar chart showing monthly sales" >

The alternative text describes the image when the image itself cannot be seen.

// uses

Where is HTML used?

Web Pages Blogs Web Applications Landing Pages Online Stores Documentation Forms Email Templates

// summary

The structure of the web.

HTML is the markup language used to describe the structure and meaning of web content. It uses elements, tags and attributes to define headings, paragraphs, links, images, forms and other parts of a document, providing the structural foundation on which CSS and JavaScript can build.