React FAQ - Javascript

React is an open-source Javascript library that is commonly used for building user interfaces (UI) and single-page applications. It was developed by Facebook and is now maintained by Facebook and a community of developers. In this React FAQ, we will answer some of the most commonly asked questions about React and Javascript.

What is JSX in React?

JSX stands for JavaScript XML, and it is an extension to plain Javascript syntax that allows you to write HTML-like code in your Javascript components. It makes it easier to write and read components and is used heavily in React. Here's an example of JSX:

const element = <h1>Hello, world!</h1>;

What is a component in React?

A component is a piece of code that is reusable and encapsulates a part of a user interface. React is heavily component-based, which means that most of the code you will write will be in the form of components. A component can be a class component or a function component.

Here's an example of a function component using JSX:

function Welcome(props) {
  return <h1>Hello, {props.name}!</h1>;
}

What is the difference between a class component and a function component?

A class component is a Javascript class that extends the React.Component class, and it has a render method that returns a React element. It allows you to use state and lifecycle methods. A function component is a Javascript function that returns a React element. It does not have state or lifecycle methods but is simpler to write and can be more reusable.

Here's an example of a class component using JSX:

class Welcome extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}!</h1>;
  }
}

What is the virtual DOM in React?

The virtual DOM is a representation of the actual DOM (the HTML that is displayed on the page) that React keeps in memory. When a component changes, instead of updating the actual DOM, React updates the virtual DOM, and then it calculates the difference between the old and new virtual DOM and updates only the necessary changes to the actual DOM. This is one of the reasons why React is so fast.

What is the difference between props and state in React?

Props (short for properties) are passed down from a parent component to a child component and are read-only. They are used to configure a component and can't be changed by the component itself. State, on the other hand, is a piece of data that is internal to a component and can be changed by the component itself. It is used to hold data that changes over time and triggers a re-render of the component.

Conclusion

React is a powerful and popular Javascript library that is widely used for building user interfaces and single-page applications. It is heavily component-based and uses JSX syntax to write HTML-like code in Javascript. React makes use of the virtual DOM to optimize performance and uses props and state to manage data flow and reactivity.