HTML (HyperText Markup Language) is the most basic building block of the Web. It defines the meaning and structure of web content. Other technologies besides HTML are generally used to describe a web page's appearance (CSS) or behavior (JavaScript).
"Hypertext" refers to links that connect web pages to one another, either within a single website or between websites. Links are a fundamental aspect of the Web. By uploading content to the Internet and linking it to pages created by other people, you become an active participant in the World Wide Web.
HTML uses "markup" to annotate text, images, and other content for display in
a Web browser. HTML markup includes special "elements" such as
<head>,
<title>,
<body>,
<header>,
<footer>,
<article>,
<section>,
<p>,
<div>,
<span>,
<img>,
<aside>,
<audio>,
<canvas>,
<datalist>,
<details>,
<embed>,
<nav>,
<search>,
<output>,
<progress>,
<video>,
<ul>,
<ol>,
<li>
and many others.
An HTML element is set off from other text in a document by "tags", which
consist of the element name surrounded by < and
>. The name of an element inside a tag is case-insensitive.
That is, it can be written in uppercase, lowercase, or a mixture. For example,
the <title> tag can be written as
<Title>, <TITLE>, or in any other way.
However, the convention and recommended practice is to write tags in
lowercase.
Cascading Style Sheets (CSS) is a stylesheet language used to describe the presentation of a document written in HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS describes how elements should be rendered on screen, on paper, in speech, or on other media.
CSS is among the core languages of the open web and is standardized across web browsers according to W3C specifications. Previously, the development of various parts of CSS specification was done synchronously, which allowed the versioning of the latest recommendations. You might have heard about CSS1, CSS2.1, or even CSS3. There will never be a CSS3 or a CSS4; rather, everything is now just "CSS" with individual CSS modules having version numbers.
After CSS 2.1, the scope of the specification increased significantly and the progress on different CSS modules started to differ so much, that it became more effective to develop and release recommendations separately per module. Instead of versioning the CSS specification, W3C now periodically takes a snapshot of the latest stable state of the CSS specification and individual modules progress. CSS modules now have version numbers, or levels, such as CSS Color Module Level 5.
JavaScript (JS) is a lightweight interpreted (or just-in-time compiled) programming language with first-class functions. While it is most well-known as the scripting language for Web pages, many non-browser environments also use it, such as Node.js, Apache CouchDB and Adobe Acrobat. JavaScript is a prototype-based, garbage-collected, dynamic language, supporting multiple paradigms such as imperative, functional, and object-oriented.
JavaScript's dynamic capabilities include runtime object construction,
variable parameter lists, function variables, dynamic script creation (via
eval), object introspection (via
for...in
and
Object utilities), and source-code recovery (JavaScript functions store their source text and
can be retrieved through
toString()).
This section is dedicated to the JavaScript language itself, and not the parts that are specific to Web pages or other host environments. For information about APIs that are specific to Web pages, please see Web APIs and DOM.
The standards for JavaScript are the ECMAScript Language Specification (ECMA-262) and the ECMAScript Internationalization API specification (ECMA-402). As soon as one browser implements a feature, we try to document it. This means that cases where some proposals for new ECMAScript features have already been implemented in browsers, documentation and examples in MDN articles may use some of those new features. Most of the time, this happens between the stages 3 and 4, and is usually before the spec is officially published.
Do not confuse JavaScript with the Java programming language — JavaScript is not "Interpreted Java". Both "Java" and "JavaScript" are trademarks or registered trademarks of Oracle in the U.S. and other countries. However, the two programming languages have very different syntax, semantics, and use.
JavaScript documentation of core language features (pure ECMAScript, for the most part) includes the following: