What is HTML, JavaScript, CSS and AJAX?

Web pages are written in HTML, the web programming language that tells web browsers how to structure and present content on a web page. In other words, HTML provides the basic building blocks for the web. And for a long time, those building blocks were pretty simple and static: lines of text, links and images.

Today, we expect to be able to do things like play online chess or seamlessly scroll around a map of our neighborhood, without waiting for the entire page to reload for every chess move or every map scroll.

The idea of such dynamic web pages began with the invention of the scripting language JavaScript. JavaScript support in major web browsers meant that web pages could incorporate more meaningful real-time interactions. For example, if you’ve filled out an online form and hit the “submit” button, the web page can use JavaScript to check your entries in real-time and alert you almost instantly if you had filled out the form wrongly.

But the dynamic web as we know it today truly came to life when XHR (XMLHttpRequest) was introduced into JavaScript, and first used in web applications like Microsoft Outlook for the Web, Gmail and Google Maps. XHR enabled individual parts of a web page — a game, a map, a video, a little survey — to be altered without needing to reload the entire page. As a result, web apps are faster and more responsive.

Web pages have also become more expressive with the introduction of CSS (Cascading Style Sheets). CSS gives programmers an easy, efficient way to define a web page’s layout and beautify the page with design elements like colors, rounded corners, gradients, and animation.

Web programmers often refer to this potent combination of JavaScript, XHR, CSS and several other web technologies as AJAX (Asynchronous JavaScript and XML). HTML has also continued to evolve as more features and improvements are incorporated into new versions of the HTML standard.

Today’s web has evolved from the ongoing efforts of all the technologists, thinkers, coders and organizations who create these web technologies and ensure that they’re supported in web browsers like Internet Explorer, Firefox, Safari and Google Chrome. This interaction between web technologies and browsers has made the web an open and friendly construction platform for web developers, who then bring to life many useful and fun web applications that we use daily.

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