React.js: Web Development Explained

React.js, also known as React or ReactJS, is an open-source JavaScript library for building user interfaces, particularly for single-page applications. It's used for handling the view layer in web and mobile apps. React allows you to design simple views for each state in your application, and React will efficiently update and render the right components when your data changes.

Developed by Facebook, React.js has gained massive popularity, due to its simplicity and efficiency. It is also maintained by Facebook and a community of individual developers and companies. React.js allows developers to create large web applications that can change data, without reloading the page. The main purpose of React is to be fast, scalable, and simple.

Understanding React.js

React.js is a declarative, efficient, and flexible JavaScript library for building user interfaces. It lets you compose complex UIs from small and isolated pieces of code called "components". React has a few key design principles that make it stand out from other JavaScript frameworks and libraries.

Firstly, React.js follows the principle of unidirectional data flow or one-way data binding. The model state is updated and then rendered to the view. This concept makes the code more stable and also boosts performance because it reduces the DOM operations. Secondly, React.js is all about components. You need to think of everything as a component. This will help you maintain the code when working on larger scale projects.

Virtual DOM in React.js

One of the unique selling points of React.js is the concept of a Virtual DOM. Developers work with a virtual browser that is more friendly than the real browser. React's virtual browser acts like an agent between the developer and the real browser.

React.js creates a memory data structure cache which computes the changes made and then updates the browser. This allows a special feature that enables the programmer to code as if the whole page is rendered on each change whereas the react library only renders components that actually change.

JSX in React.js

JSX is a syntax extension for JavaScript. It is used with React to describe what the UI should look like. JSX may remind you of a template language, but it comes with the full power of JavaScript. JSX produces React “elements”.

While it is not necessary to use JSX in React development, it is recommended because it is a concise and familiar syntax for defining tree structures with attributes. It also gives a clear understanding of the rendering logic, which is because it is closer to JavaScript than HTML.

React.js Components

Components are independent and reusable bits of code. They serve the same purpose as JavaScript functions, but work in isolation and returns HTML via a render function. Components are the heart of React.js. In React, a web application is divided into small parts called components. Every component has its logic and controls, and they can be reused throughout the application, which in turn makes the development process much more efficient.

There are two types of components in React.js: Functional components and Class components. Functional components are simply JavaScript functions. We can create a function that takes props as an argument and returns a React element. Class components, on the other hand, require you to extend from React.Component and create a render function which returns a React element.

Props in React.js

Props is a special keyword in React, which stands for properties and is being used for passing data from one component to another. But the important part here is that data with props are being passed in a uni-directional flow. (one way from parent to child)

Furthermore, props data is read-only, which means that data coming from the parent should not be changed by child components. It is important to note that in React, data flows from parent component to child components. The data in the props is used by the child component but cannot be modified by the child component.

State in React.js

State is a data structure that starts with a default value when a Component mounts. It may be mutated across time, mostly as a result of user events. When the state of a component changes, the component re-renders.

State is similar to props, but it is private and fully controlled by the component. State is reserved only for interactivity, that is, data that changes over time. Unlike the props, a component's state is not passed from the outside but is maintained within the component itself. A component can decide to pass its state down as props to its child components.

React.js Lifecycle

Each component in React has a lifecycle which you can monitor and manipulate during its three main phases. The three phases are: Mounting, Updating, and Unmounting.

The Mounting phase is being called when an instance of a component is being created and inserted into the DOM. The Updating phase is being called when a component is being re-rendered as a result of changes to either its props or state. The Unmounting phase is being called when a component is being removed from the DOM.

Mounting Lifecycle Methods

In the mounting phase, there are four methods that are being called in the following order: constructor(), static getDerivedStateFromProps(), render(), and componentDidMount(). The render() method is the most used lifecycle method. It is a pure function, meaning that at any point in time, calling the render method will return the same output given the same state/props.

The componentDidMount() method is called once all the child components have been rendered and the component has been inserted into the DOM tree. This method is a good place to perform setup work like creating timers or sending AJAX requests for data.

Updating Lifecycle Methods

When a component's props or state change, it gets re-rendered. There are five built-in methods that gets called when a component is updated: static getDerivedStateFromProps(), shouldComponentUpdate(), render(), getSnapshotBeforeUpdate(), and componentDidUpdate().

The shouldComponentUpdate() method allows you to opt-out of rendering for certain updates for performance optimization. It is called before the re-rendering process starts, enabling you to decide whether or not React should continue with rendering.

Unmounting Lifecycle Methods

The final phase of the lifecycle if called when a component is being destroyed and removed from the DOM. There is one built-in method, componentWillUnmount(), that is called in this phase.

The componentWillUnmount method is the last function to be called immediately before the component is removed from the DOM. It is generally used to perform clean-up for any DOM elements or timers created in componentDidMount().

React.js Hooks

Hooks are a new addition in React 16.8. They let you use state and other React features without writing a class. Hooks are functions that let you “hook into” React state and lifecycle features from function components. Hooks don’t work inside classes — they let you use React without classes.

React provides a few built-in Hooks like useState, useEffect, useContext, useReducer, useRef, useMemo, useCallback, useImperativeHandle, useLayoutEffect, and useDebugValue. You can also create your own Hooks to reuse stateful behavior between different components.

useState Hook

The useState is a Hook (function) that allows you to have state variables in functional components. You pass the initial state to this function and it returns a variable with the current state value (not necessarily the initial state) and another function to update this value.

In classes, the state is always an object, and you can store multiple values in that object. But with useState, you can have a state variable for every value you want to store. One function - one value. But you can call useState as many times as you want, for as many values as you want.

useEffect Hook

The Effect Hook, useEffect, adds the ability to perform side effects from a function component. It serves the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount in React classes, but unified into a single API.

When you call useEffect, you’re telling React to run your “effect” function after flushing changes to the DOM. Effects are declared inside the component so they have access to its props and state. By default, React runs the effects after every render — including the first render.

React.js Tools and Ecosystem

React.js has a rich ecosystem that includes various tools and libraries that enhance its development process. Some of these tools include Redux, React Router, and Next.js. These tools are not part of the React.js library but are often used with React to build real-world applications.

Redux is a predictable state container for JavaScript apps. It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test. React Router is a standard library for routing in React. It enables the navigation among views of various components in a React Application, allows changing the browser URL, and keeps the UI in sync with the URL. Next.js is a popular framework for server-rendered React applications.

Redux in React.js

Redux is a predictable state container designed to help you write JavaScript apps that behave consistently across client, server, and native environments and are easy to test. While it’s mostly used as a state management tool with React, you can use it with any other JavaScript framework or library.

Redux is a tool for managing both data-state and UI-state in JavaScript applications. It is not tied to React and can be used with any JavaScript framework or library. It is a small library (2KB, including dependencies), but it has a large ecosystem of addons, and is incredibly flexible.

React Router in React.js

React Router is a standard library system built on top of the React and used to create routing in the React application using React Router Package. It provides the synchronous URL on the browser with data that will be displayed on the web page. It maintains the standard structure and behavior of the application and is used for developing single page web applications.

React Router has a simple API. It uses the concept of Routes defined in your component and then rendering components based on the current browser URL. If you have been working with React for a while, you are familiar with the concept of components and how they are a central part of React. React Router takes this concept to the next level.

Next.js in React.js

Next.js is a lightweight framework for static and server-rendered applications. It's built on top of React, Webpack, and Babel. It is a great tool to build your next website. It has many great features and advantages, which can make Nextjs your first option for building your next web application.

Next.js provides an integrated toolset for server-rendered React applications, automatic code splitting, simple client-side routing, built-in CSS support, development environment which supports Hot Module Replacement, and many more. It is a tool for building server-side rendered and static web applications.