The Birth of React

This library was born in the hallways of Facebook, when the company was grappling with the challenge of managing increasingly dynamic and complex user interfaces. The need for an agile and efficient solution drove its development, first tested on the News Feed in 2011. That early success paved the way for its wider adoption: other companies, like Netflix, soon picked it up to build interfaces that were fast, modular and easy to maintain.

Fundamentals

React is a JavaScript library. That means it's not a full framework that dictates how to structure an entire project, but rather a set of tools designed to solve a specific problem: building interactive interfaces out of independent components.

The name React isn't an acronym or abbreviation, it's a proper name that reflects the idea that the interface "reacts" quickly and efficiently to changes in data.

At the heart of this technology is the idea of reusable components. These are pieces of code that encapsulate structure, style and logic, and can be recombined like building blocks. What sets React apart is that it doesn't redraw everything on screen every time something changes, only what's actually needed, thanks to a system called the Virtual DOM.

Instead of refreshing the whole page every time something changes, a slow and expensive operation, this technology keeps a virtual copy in memory. When a piece of data changes, it compares the previous version against the new one and updates only what's needed. This guarantees performance and efficiency even in complex applications.

Another pillar is JSX, a syntax that blends JavaScript with HTML-like tags. JSX isn't mandatory, but it makes components far easier to read and write, since it lets you describe the interface declaratively, in a visual language developers already know.

It's worth noting that this is a Front-End tool, that is, client-side. It doesn't handle server operations or databases; its strength lies in connecting to any kind of back-end, whether monolithic or microservices-based.

Monoliths and Microservices

A monolithic project is one where the whole system, interface, business logic, server and database, is deployed as a single unit. This makes it easier to understand and deploy, but it can make scaling harder.

Microservices, on the other hand, split the application into smaller, independent pieces, each handling one specific function. This brings flexibility and granular scalability, although it demands a bigger upfront investment in infrastructure and coordination.

React is used on the visual side of an application, not on the server. Even so, it fits smoothly into different kinds of systems. In a monolithic system, where the front (visual layer) and back (server) live together in a single block, it helps keep the interface clearer and more organized. It also works perfectly in microservices systems, where everything is split into independent pieces: its components fit right in, since they're also built as reusable blocks that connect to one another.

Components: The Building Blocks of Interactivity

Reusable components are the foundation of this technology. They are independent pieces dropped into each view with their own design and independent logic. A "Like" button, for example, is a single block of code written once, which can then be used anywhere in the application with the same look and the same function, just by inserting it. That saves work and keeps everything tidier. What's more, if we want to change its logic or appearance, we only need to modify it once for that change to show up everywhere it's used.

That's the real strength of this model: reusability. The same block can be repeated in many parts of the application and will always behave the same way. By combining different components, like menus, forms or comment lists, complete applications get built that are easier to understand and maintain.

State and Props

For everything to work dynamically there are two key ideas: state and props.

State is the data a component manages on its own, which can change through interaction. If someone clicks "Like", that internal value changes and the screen responds by showing the new result. That's how the interface reacts on its own without us having to update everything by hand.

Props, on the other hand, are the information a component receives from a larger one. A comment, for example, might receive the username and message text as props. It's worth noting that this data doesn't get changed inside the component that receives it. If something needs to change, the parent component updates it and passes it back down to the child. That's what keeps everything orderly and predictable.

Hooks

For a long time, classes were used whenever a component needed to store state. That changed in 2019 with the arrival of Hooks, which simplified the way code gets written.

The most common one is useState, which lets you store and update a value with ease. For example:

const [count, setCount] = useState(0)

This one line creates a counter that starts at zero and can keep incrementing. There are other Hooks too, like useEffect, used to trigger actions when something changes, or useContext, which lets you share data across several components. Today, Hooks are the standard, and they make coding clearer and more direct.

Integrating with APIs

React's real power shows up when the interface built with it connects to APIs. An API works like a waiter at a restaurant: it takes the customer's order to the kitchen and then brings back the food. The same thing happens in applications: the visual layer asks the server for data, and the API returns the response.

That information almost always travels in JSON format, which is easy for the application to work with. That's how everything from simple projects to massive systems gets built. It works both with a single server and with several separate services working together.