Can you run HTML code?

Yes, it is possible to run HTML code. HTML, which stands for Hypertext Markup Language, is not a programming language but rather a markup language used to structure and present content on the web. While HTML by itself doesn’t “run” like a traditional programming language, web browsers are designed to interpret HTML code and render the corresponding web page accordingly. When you load a web page, the browser reads the HTML code and uses it to build the rendered page that you actually see.

Table of Contents

How is HTML interpreted and displayed?

When a web browser loads an HTML file, it goes through a sequence of steps to interpret the code and render the page:

The browser reads the raw HTML code from top to bottom.
It parses the code to identify HTML elements like tags, attributes, text content, etc.
It constructs a Document Object Model (DOM) in memory to represent the page structure.

The browser’s rendering engine uses the DOM and CSS styling rules to calculate geometries, layout, and styling for each element.
The visual pixels are painted to the screen to display the desired page.

This overall process is commonly referred to as “rendering the HTML.” The browser goes through these steps each time a page is loaded or refreshed. HTML provides the basic structure and semantics, while CSS and JavaScript add further styling and interactivity.

HTML tags and elements

HTML documents contain HTML elements that are denoted using angled brackets like <tagname>. Most elements consist of an opening and closing tag pair like <p>paragraph content</p>. The element’s name defines its semantic meaning, while attributes provide additional properties.

Here are some common HTML elements and their purposes:

<h1> to <h6> – Headings and document structure

<p> – Paragraphs of text
<div> – Block container for grouping elements
<span> – Inline container for wrapping text

<img> – Images
<a> – Links
<table>, <tr>, <td> – Tables

<ol>, <ul>, <li> – Numbered and bulleted lists
<form>, <input> – Forms

There are over 100 different HTML elements available to structure content semantically. Each element has its own defined purpose and usage.

How HTML is “run”

While HTML itself isn’t a traditional programming language, we can consider a web browser loading and rendering HTML code as “running” that HTML code. Here’s a more technical explanation of how it works:

The browser makes an HTTP request to load the HTML file from a web server.
The server locates and returns the HTML file to the browser.

The browser parses the raw HTML code and constructs a DOM tree.
It combines the DOM with CSS rules to create a render tree.
The render tree goes through layout to compute geometries and positions.

Finally, the browser’s rendering engine paints pixels to the screen.

So in summary, the browser “runs” HTML code by processing it through a sequence of steps like a software program. The rendered page depends on how the browser interprets and executes the HTML code. HTML provides the structure while CSS and JavaScript enable further functionality.

Displaying Dynamic Content

While static HTML alone can only display static content, combining it with other web technologies allows for dynamic document content:

JavaScript – Can manipulate HTML DOM at runtime to update content, styling, animations, etc.
CSS – Can alter styling and layout based on user interaction and events.
Web APIs – Can fetch dynamic data from databases and servers to inject into page.

Server-side code – Can generate HTML with dynamic data on the server before sending to browser.

For example, JavaScript code can listen for events like button clicks. When a user clicks a button, JavaScript can use DOM methods like document.getElementById() and element.innerHTML to update parts of the HTML with new content. This enables dynamic user experiences.

Client-Server Model

The client-server model is used to deliver dynamic HTML web pages:

The client is the web browser that makes requests and displays the HTML.
The server is the computer that stores and serves the HTML files.

This separation of concerns enables dynamic HTML generation:

Browser requests an HTML page from the server.
Server runs application code to dynamically generate the HTML.
Server returns the generated HTML to the client.

Browser renders the HTML like normal.

For example, a server can run PHP code to query a database and use the results to generate the HTML. The client receives pre-rendered HTML produced dynamically on the server.

Common Server-Side Languages

Some common server-side languages used to generate dynamic HTML are:

PHP – Scripting language that can create HTML embedded with PHP code.
ASP.NET – Microsoft framework to build web apps with .NET languages like C#.
Ruby on Rails – Web app framework written in Ruby.

Node.js – JavaScript runtime to build server apps with JavaScript.

These languages can utilize templates, data sources like databases, and logic to produce HTML dynamically before sending to the client. This enables content personalization, real-time updates, interactivity, and more.

Loading HTML from JavaScript

JavaScript running in the browser can also request and load HTML snippets dynamically:

Make AJAX calls to fetch HTML from the server.
Insert received HTML into the DOM using methods like element.innerHTML.
JavaScript libraries like React allow creating HTML with JavaScript.

For example, a single page app might use React to render components into the DOM dynamically based on user interaction. This allows updating parts of the UI without full page reloads.

Executing JavaScript from HTML

HTML can also execute JavaScript code using elements like:

<script> – Adds inline JS code inside HTML.

<a onclick=””> – Calls JS function when link clicked.
<button onclick=””> – Calls JS on button click.
<img onload=””> – Triggers JS when image loads.

For example:

  <button onclick="alert('Hello World!')">Click Me!</button>

This allows HTML to execute JavaScript behaviors added through event attributes and bindings.

HTML APIs

JavaScript code can also interact with HTML using DOM APIs like:

document.getElementById() – Find element by ID
element.innerHTML – Get/set inner HTML
element.style – Get/set CSS styles

element.addEventListener – Attach event handler
document.createElement() – Create new element

This allows JavaScript to dynamically modify HTML and CSS styles, react to events, build UI components, animate elements, and more.

HTML Templating

HTML templating systems like Handlebars allow writing HTML templates with placeholders that can be filled dynamically with data at runtime:

“`html

{{name}}: ${{price}}

“`

JavaScript code can then inject data like products from a database into the template placeholders. The final rendered HTML is produced by merging the template + data.

Preprocessing HTML

HTML preprocessors like Pug (formerly Jade) allow writing HTML more concisely with a cleaner syntax. Pug code:

“`pug
ul#productlist
each product in products
li #{product.name}: $#{product.price}
“`

Gets compiled into standard HTML before sent to the browser. This allows using tools like Pug as an abstraction above HTML.

Static Site Generators

Static site generators like Jekyll allow authoring sites using templated HTML+Markdown content. At build time, the HTML is parsed and generated into static .html files for deployment. For example:

Write pages using HTML + Markdown templates.
Markdown gets converted to HTML.

Templates get injected with data.
Static HTML files get generated for deployment.

This allows separation of concerns with templated HTML and Markdown while optimizing for static content delivery.

Delivering HTML Over HTTP

The primary way HTML is delivered from servers to clients is using HTTP:

Browsers request HTML pages from servers using HTTP GET.
Server locates the .html file and delivers it in the HTTP response.

HTTP headers describe metadata like content type.
HTTP status codes indicate outcomes like 200 OK.

For dynamic sites, servers may run application code to produce the HTML before returning it over HTTP. Modern web frameworks make it easy to generate and deliver HTML using HTTP APIs.

HTML Frameworks and Tools

Many tools and frameworks exist to help build HTML sites and applications:

React – JavaScript library for building UIs with components.
Angular – Framework for building single page applications.

Vue – Progressive framework for UIs.
Bootstrap – CSS framework for responsive layouts.
Bulma – CSS framework based on Flexbox.

jQuery – JavaScript library for DOM manipulation.

These provide commonly needed building blocks and patterns like navigation, forms, buttons, grids, etc. so you don’t have to write everything from scratch.

HTML Semantic Elements

HTML includes semantic elements that describe their meaning rather than just presentation:

<header>
<footer>
<article>

<section>
<nav>

This allows writing HTML that describes the data more accurately. It also enables better accessibility and opportunities for styling/interaction.

Accessibility

HTML provides ways to make content more accessible:

<alt> text for images
Semantic elements like <header>

ARIA roles for dynamic content
Keyboard/screen reader support
Color contrast

By writing accessible HTML, sites can reach users with disabilities. This includes those using screen readers, keyboard navigation, or other assistive technologies to browse the web.

Validation

HTML can be validated against standards like HTML5 using validators like:

W3C Validator – Validates HTML/XHTML standards

HTML5 Validator – Checks HTML5 conformance

Fixing errors and warnings ensures proper HTML syntax. Valid HTML also provides benefits like:

Better accessibility

Improved SEO
More consistent rendering

Following web standards improves compatibility across different browsers and devices.

Conclusion

While HTML is not a traditional programming language, web browsers essentially “run” HTML code by processing and rendering it into dynamic web pages. HTML provides structure and semantics, while CSS and JavaScript add further styling and interactivity behaviors. A variety of templating systems, preprocessors, frameworks, and tools exist to enhance working with HTML. Following standards and best practices allows HTML to be run securely and reliably across platforms and devices.