What is Front-End Development: Key Technologies and Concepts

What do you see when walking around and staring at the cityscapes? Probably, among the first things are shop fronts, shining and beckoning, created to draw you inside. You choose the most attractive, open the door, and enter.

The same happens on the web. Surfing the Internet for things you need, you come up with the most engaging site, open it, and there you are.

But if the shop windows can show you what’s inside it, invite you to touch the goods, understand that it’s different for websites. What elements are hiding under the hood of the website’s visible elements, how do they interact with a user, each other, and the system behind it all? Let’s find this out.

What is front-end development? Front end vs back end

The website’s front end is everything you see and can interact with using a browser. So, creating this visual part is called front-end development. You could even say that designers creating user interfaces and planning experiences are also front-end developers, as they are working in collaboration on the same part of the project.

To create the front end, engineers use the combination of HTML (for basic page structure and content), CSS (for visual editing), and JavaScript (for making websites interactive). The same set of tools is used to create progressive web apps –  mobile apps that look and feel like a native one but are created with the use of front-end technologies. There’s more about that in the linked article.

On the other hand, the back end is everything that happens, well, backstage. It contains servers where your web pages are located and the underlying logic that governs the website’s functions and processes. We have an in-depth description of the inner workings of web applications if you want to check it out.

The back end is built using a different set of technologies, including Java, PHP, Ruby, C#, and sometimes JavaScript, which we’ll explain in a corresponding section.

A process of web-request and response

A process of web-request and response

The basic toolset for a front-end is well-defined: HTML, CSS, and JavaScript. The frontend development technologies may be however extended with package managers, CSS preprocessors, frameworks, and many more.

HTML: the key front-end technology

HTML (or Hypertext Markup Language) is a computer language designed to create websites that later can be explored by anybody who accesses the Internet. HTML is normally employed to structure a web document. It defines such elements as headlines or paragraphs and enables embedding images, video, and other media.

How HTML works. HTML is composed of a series of shortcodes called tags, normalized into a text-file by a site creator. The text is then stored as an HTML file and observed through a browser. The browser scans the file and interprets the text into a visible form, and in the best case, renders the page as the designer had planned.
  • HyperText is the way by which we travel across the web by clicking hyperlinks – specific texts taking you to other pages. Hyper means it’s non-linear, which allows for moving to any other place, as there is no predefined order to do so.
  • Markup determines the qualities that HTML tags apply to the text inside them. Tags mark it as a particular type of text.
  • As a Language, it holds code words and syntax like any other language.
For example:


The example of HTML code

The text between <html> and </html> specifies the web page, while the text between <body> and </body> determines the visible content.

<!DOCTYPE html> on the top is the Document Type Declaration for HTML5. If it’s not included, different browsers will render it in their way.

This is how we gradually move to HTML5.


Since its initial release in 1991, HTML has undergone many updates. HTML5 released in 2014. It has added such features as offline media storage support, more precise content elements (i.e. header, footer, navigation), and support for audio and video embedding.

CSS: Styling your facade

CSS (or Cascading Style Sheets) is a style sheet language. It’s applied to define how HTML elements are supposed to be presented on a webpage in terms of design, layout, and variations for diverse devices with different screen sizes. CSS masters the layout of numerous different web pages at a time.

How it works. CSS interacts with HTML elements, the components of a web page.
  • To communicate with HTML, CSS uses selectors. A selector is the part of CSS code defining which HTML piece the CSS styling will impact.
  • A declaration contains properties and values that are employed by the selector.
  • Properties define font size, color, and margins. Values are the settings for these properties.
If we take an example,


The example of CSS code

P (for paragraph) is selector, {  font-size:24px;  color:blue;  } is a declaration, font-size: and color: are properties, while 24px; and blue; are values.

CSS is written in plain text over a text editor or word processor on a computer. If you were to examine how the CSS code is implemented to HTML content, there are three ways to do so:
  • External style sheets are stored as .css files and can be applied to define the appearance of a whole website via a single file, instead of putting extra instances of CSS code to every HTML element which has to be modified. To use an external style sheet, .html files need to contain a header section that connects to the external style sheet.
  • Internal style sheets are CSS directions put straight into the header of a particular .html page.
  • Inline styles are snippets of CSS recorded into HTML code itself.
CSS frameworks. A CSS framework is a set of default CSS and HTML files. It extends a front-end developer’s capabilities for website design. In addition to assisting while building a responsive design, CSS frameworks also present distinct and symmetric layouts, saving developers from writing code from ground zero at every occasion. They are usually considered a good choice to fit diverse platforms and screen sizes. With common user interface components, grid systems, layouts, and many other features, CSS frameworks considerably accelerate development workflow. Many frameworks exist in the CSS Universe:
  • Full featured (Bootstrap, Foundation, Semantic UI, and more),
  • Aimed at Material Design: (Materialize and Material Design Lite), and
  • Lightweight (Pure).
We won’t describe them all. You can examine our comparison table instead.

Most popular CSS frameworks

Most popular CSS frameworks

In case you want to explore these CSS frameworks in detail, check out our article on Most Popular Responsive CSS Frameworks.

Preprocessors - Sass and LESS. Drafting CSS is routine, while short tasks such as looking up color values, closing tags, or any other repetitive operations take a lot of time. That’s where a preprocessor comes in handy. A CSS preprocessor is a scripting language that expands CSS and assembles it into general CSS.

Sass and LESS are the most common preprocessors. They share some common basics, such as:
  • Syntax elements and
  • Backward compatibility with normal CSS files.
However, there are also a lot of differences between them.
  • Sass means Syntactically Awesome Style Sheets. Sass runs on Ruby and is rendered on the server side. Due to its Ruby language origin, the installation is provided via so-called gems (multiple Ruby/Rails libraries).
  • LESS stands for Leaner Style Sheets. It’s a JavaScript library and is rendered on the client side in the browser. Developers choose LESS much more regularly when using JavaScript with style sheets. It resembles composing regular CSS. The technology allows for reusing pieces of CSS within LESS files.

DOM: the web page structure

The Document Object Model (DOM) is defined as a programming interface for HTML and XML documents. It interprets the page so that programs can modify the document structure, style, and content. The DOM renders the document as nodes and objects, enabling programming languages to connect to the page.

The HTML DOM tree of objects

The HTML DOM tree of objects

Source: W3Schools

How it works. Consider a web page as a document that can be either presented in the browser window or as the HTML source code. The Document Object Model (DOM) represents this document so it can be modified. The DOM is an object-oriented representation of the web page, which can be altered with a scripting language like JavaScript.

The DOM must adhere to W3C and WHATWG standards that are executed in most current browsers. The modern DOM is built using multiple APIs that work together. The core DOM specifies the objects that entirely explain a document and the objects within it.

JavaScript: making the Web alive

JavaScript (JS) is one of the most popular scripting languages. It’s mostly renowned for providing a full stack of technologies for both front-end and back-end development. As we are talking about the first one, it’s applied to make web pages dynamic.

How JavaScript works. JS boosts a website’s overall interactivity. It enables modeling animated UI components such as image sliders, pop-ups, extensive site navigation menus, and more. JavaScript provides a website with extended functionality that isn’t otherwise achievable with HTML and CSS alone. JavaScript allows web pages to reply to users’ actions and dynamically refresh themselves. Thanks to JavaScript, this process doesn’t demand a page reload to alter its representation.

JavaScript frameworks and libraries and why we need them

Those who are just entering this field of expertise may think that frameworks and libraries do the same thing, allowing different visual elements to interact with each other. And let’s be honest: It’s not too far from the truth. However, there are a few distinguishing peculiarities. So, let’s define what makes a JS framework, what a JS library is, and what purpose they both serve.

Frameworks are templates to create a website or a web application. They provide a structure (such as a skeleton or scaffolding) on which to arrange the whole project. While the framework sets the page templates, they build the structure with particular allocated areas to embed a framework code in.

So, JavaScript frameworks are complete sets of tools to form and arrange a website or web application.

Libraries are sets of prewritten code snippets used and reused to implement core features of JavaScript. The snippet can be easily integrated into an existing project code when necessary.

So, libraries are specialized tools for particular coding needs, not an all-purpose machine for grooming the whole existing project.

Main frameworks and libraries to know

Let’s start with frameworks:

Angular is a front-end framework powered by Google that is compatible with most of the common code editors. Angular is intended to create dynamic, single-page web applications (SPAs), and progressive web-apps. Upon its initial release, the framework was most appreciated for its ability to convert HTML-based documents into dynamic content. Angular is among the most popular front-end frameworks. You can explore this topic in our article on the pros and cons of Angular development.

Vue.js is yet another open-source framework for SPAs. It employs a component-based development model and enables attaching components to a project. Vue.js is an example of a library that is more of a framework. To utilize Vue.js, knowledge of HTML and CSS is an absolute requirement. It suggests a whole bunch of templates and patterns applied in development. Vue is primarily recognized for the small size of documents and HTML-based syntax. Again, to immerse yourself in Vue.js advantages and disadvantages click the link.

Ember.js is a framework for SPAs, mobile, and desktop applications. It uses the model-view-view-model (MVVM) pattern. Ember tools enable designing a development environment, while its command-line interface gives tools for script automation.

And now let’s outline a few libraries:

React is an open-source library for building dynamic user interfaces, born and bred by Facebook. The framework is applied to create web-applications with multiple dynamic components. It relies on JavaScript and JSX, a Facebook PHP language extension. React enables building reusable HTML elements for the front end. React also includes React Native, a dedicated cross-platform mobile development framework. To discover more about the pros and cons of React and React Native, consider exploring our article on this subject.

jQuery, in turn, is aimed at controlling HTML documents. It has a simple API to control events and design animation in browsers. Aside from that, jQuery is applied to manipulate the Document Object Model (DOM) and serves as a plugin development tool as well. It also comes with a lighter cross-browser library, jQuery UI for a mobile framework jQuery Mobile and for graphic interface construction.

D3.js is a data-driven library for data visualization. By tying temporary data to DOM and implementing data-driven changes to the document, the library enables managing data and making dynamic data visualizations. It can uphold and process large datasets and dynamic responses for interaction and animation. D3’s functional style permits code reusing and runs with CSV and HTML.

As we see, JavaScript’s extensive libraries have broad functionality, being a one-stop solution for front-end developers. But the thing is, it’s not a matter of substitution or favoring libraries over frameworks or vice versa. There’s always a place for both a library and a framework.

If you’re starting with the front end, it would be reasonable to begin with libraries since they have a milder learning curve. Upon capturing the basics from a few of them, learners can proceed to frameworks, as they require a greater understanding of JS fundamentals.

JavaScript for the back end

Speaking of JavaScript as an end-to-end development environment, we must mention its back-end implementation. Since JavaScript is so popular, the software engineering world adapted JS to back-end specifics.

For web server-side development with JavaScript, Node.js has probably become one of the most prominent tools. However, it’s neither a framework nor a library. Node.js is a runtime environment based on Chrome’s V8 JavaScript engine. For a deeper understanding of Node.js, feel free to read our article about the Pros and Cons of Node.js web app development. Or just watch our video on Good and Bad of Node.js.
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Communication between front end and back end

The front end doesn’t exist in isolation from the back end, or the server that actually provides data. Let’s have a look at the concepts in terms of client-server messaging.

Asynchronous operations

In the 2010s, one of the main concepts describing the way the web worked was AJAX. The term stands for Asynchronous JavaScript and XML. Basically, it’s a complex of techniques to create websites and web applications. Let’s look at the key components that make up AJAX.

Asynchronous - the fundamental aspect of the whole toolkit. The crucial role of the approach is to renew web content... asynchronously. It means that a user’s web browser doesn’t have to reload a whole web page when a small part of the content on the page requires some change, e.g. you don’t have to reload the entire eCommerce products page to apply an additional filter to search results. You just need these results to be updated.

JavaScript - JavaScript employs website automation processes so web developers don’t have to separately edit each case of the process appearing on a page. It’s used particularly to create, add, and manage dynamic website content. After all HTML and CSS processes are handled, JavaScript then runs real-time updates while a visitor is viewing an interactive content page.

XML (or Extensible Markup Language) allows for transmitting data put on the page to the browsers that view it. That’s important for specific computer systems that often can’t interact with data formatted by a different system. In this case, XML allows for avoiding incompatibility while saving data in plain text format between XML tags. This way, XML suggests a means of storing, moving, and sharing data that doesn’t rely on a singular software or hardware system. Since XML is getting older, freeing the way to newer data formats, you can run AJAX with JSON, which is shorter and easier for humans to read.

Today, AJAX isn’t as commonly discussed in the front-end community due to the simple fact that asynchronous web page rendering comes out of the box in all major front-end frameworks that we discussed above.

How asynchronous updates work. Let’s say, a user clicks a button. The client sends a request to a server-side script with XML/JSON in the background as a user keeps viewing the page. The server side obtains the data from JavaScript, reaches the database if required, and processes the data. With XML/JSON anew, it sends the data back to the initial client-side page that executed the entry. A callback, performed by JavaScript, captures the data and refreshes the web page component that needed changes.

REST and GraphQL

REST stands for Representational State Transfer. Basically, it’s a lightweight architectural style applied to messaging between a client (front end) and a server (back end). RESTful services and APIs are web services following the REST architecture.

For example, a developer has to build a web app that shows all social media friends in a particular order. A front-ender can create requests to Facebook’s RESTful API to view the friends list and pass that data back. Any service using RESTful APIs resembles this general process, different only are data retrieved and returned. REST is a plain collection of guidelines and practices that establish rules to interact with a web service.

The main idea behind REST is that the server doesn’t care what happens to the client. Instead, REST messages contain all the needed information for a server to return the needed data and forget about this operation. To learn more about different messaging formats and an older SOAP standard, check the dedicated article.

GraphQL is the modern spin on messaging. It’s a language for querying databases from client-side applications. On the server side, GraphQL defines how to display the data to the client and caters to various types of clients and their data needs. If you want to get a deeper dive into this topic, read our article on GraphQL Core features.

More practices that go into front-end development

So, we outlined the basic elements for front-end development. However, there are many more terms and concepts that a front-end developer must understand.

Responsive design

As increasingly more people access the Internet from their mobile devices rather than from desktops, responsiveness is a must. Responsive design means that the web layout (including functionality and content) adjusts to the screen size and hardware.

For instance, when a website is visited from a desktop computer with a big monitor, a user gets numerous columns, heavy graphics, and UI designed particularly for mouse and keyboard. On mobiles, the same website appears as a single column adjusted for touch interaction, but with the same base data. Have a look at our article on responsiveness to get a better idea.

Accessibility and inclusivity

Accessibility means making a website available to as many people as possible. This concept does not only include all kinds of disabilities that people have, such as visual, cognitive, hearing, or mobility impairments. It also covers matters of law, compliance standards, different mobile devices, and different types of network connections. Our overview of accessibility practices provides broader awareness of the topic.

Let's Recap

We admit that stepping into front-end technologies can be a little dazzling, even with the basics. So, let’s sum up what we’ve learned.

HTML (or Hypertext Markup Language) is a computer language for building websites. It’s usually applied to structure a web document.

CSS (or Cascading Style Sheets) is a style sheet language. It’s used to specify the representation of HTML elements on a webpage. CSS scope includes the design, layout, and variations in display for diverse devices and screen sizes.

DOM (or Document Object Model) is a programming interface for HTML and XML documents. It contains the page info so that programs can change the document structure, style, and content.

JavaScript is a scripting language. In the front-end, it’s used to make web pages dynamic. Additionally, it provides full-stack technologies with libraries and frameworks for both client-side and server-side scripting.

AJAX. AJAX (or Asynchronous JavaScript and XML) is a complex of techniques to create websites and web applications with dynamically uploaded content without creating a new data record.

Of course, there are many more technologies, skills, and overall knowledge that a beginner is set to learn. However, we hope that this article created a path for the journey into the forest of front-end development to keep the traveler from getting lost.


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