ReactJs
All the fundamental React.js concepts
React.js is an open-source JavaScript library that is used to build user interfaces (UI). It was developed by Facebook and has become one of the most popular UI libraries available. React allows developers to build fast and efficient UIs using a component-based architecture. In this article, we will discuss all the fundamental React.js concepts that you need to know to get started with building UIs using React.
Components
In React, everything is a component. A component is a self-contained unit of code that is responsible for rendering a specific part of the UI. Components can be nested inside other components, which makes it easy to build complex UIs. There are two types of components in React: functional components and class components.
Functional Components
Functional components are the simplest type of component in React. They are functions that return JSX (JavaScript XML) to define the UI. Functional components are useful when you only need to render UI and don’t need to manage state.
Here’s an example of a functional component:
javascript
function Welcome(props) {
return <h1>Hello, {props.name}!</h1>;
}
Class Components
Class components are more powerful than functional components. They are classes that extend the React.Component class and use a render method to define the UI. Class components are useful when you need to manage state or use lifecycle methods.
Here’s an example of a class component:
javascript
class Clock extends React.Component {
constructor(props) {
super(props);
this.state = { date: new Date() };
}
componentDidMount() {
this.timerID = setInterval(
() => this.tick(),
1000
);
}
componentWillUnmount() {
clearInterval(this.timerID);
}
tick() {
this.setState({
date: new Date()
});
}
render() {
return (
<div>
<h1>Hello, world!</h1>
<h2>It is {this.state.date.toLocaleTimeString()}.</h2>
</div>
);
}
}
JSX
JSX is a syntax extension for JavaScript that allows you to write HTML-like code in your JavaScript code. It is used to define the UI in React components. JSX makes it easy to create components that closely resemble the final HTML output.
Here’s an example of JSX:
javascript
const element = <h1>Hello, world!</h1>;
Props
Props (short for “properties”) are used to pass data from a parent component to a child component. They are read-only and cannot be modified by the child component. Props are useful when you need to customize a component’s behavior or appearance.
Here’s an example of props:
javascript
function Welcome(props) {
return <h1>Hello, {props.name}!</h1>;
}
const element = <Welcome name="John" />;
State
State is an object that represents the internal state of a component. It can be modified by the component and can trigger a re-render of the UI. State is useful when you need to manage dynamic data in a component.
Here’s an example of state:
javascript
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { count: 0 };
}
handleClick() {
this.setState({ count: this.state.count + 1 });
}
render() {
return (
<div>
<p>Count: {this.state.count}</p>
<button onClick={() => this.handleClick()}>Increment</button>
</div>
);
}
}
Lifecycle Methods
Lifecycle methods are methods that are called at specific times during a component’s lifecycle. They allow you to run code at specific times, such as when a component is mounted or updated. Some common lifecycle methods in React include componentDidMount, componentWillUnmount, and shouldComponentUpdate.
Here’s an example of a lifecycle method:
javascript
class Example extends React.Component {
constructor(props) {
super(props);
this.state = { count: 0 };
}
componentDidMount() {
console.log('Component mounted');
}
componentWillUnmount() {
console.log('Component will unmount');
}
render() {
return (
<div>
<p>Count: {this.state.count}</p>
<button onClick={() => this.setState({ count: this.state.count + 1 })}>
Increment
</button>
</div>
);
}
}
Virtual DOM
The virtual DOM is a lightweight copy of the real DOM (Document Object Model). It is used by React to improve performance by minimizing the number of updates to the actual DOM. When a component’s state or props change, React compares the virtual DOM with the previous version to determine the minimum number of changes required to update the actual DOM.
Event Handling
Event handling in React is similar to event handling in HTML. You can add event handlers to elements using the onClick attribute, for example. The difference is that event handlers in React are written in JavaScript rather than inline HTML. Additionally, event handlers in React use synthetic events, which are lightweight representations of browser events.
Here’s an example of event handling:
javascript
class Button extends React.Component {
handleClick() {
console.log('Button clicked');
}
render() {
return (
<button onClick={() => this.handleClick()}>
Click me
</button>
);
}
}
Conclusion
These are the fundamental concepts of React.js that every beginner should know. By understanding these concepts, you can start building UIs using React and take advantage of its power and flexibility. React can be a bit overwhelming at first, but with practice and experience, you’ll be able to build complex UIs with ease.