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What are components?

Components are building blocks of any Next.js application. They are the smallest reusable chunks of code which represent a part of the user interface. In Next.js, Components are primarily written in JavaScript using React, a popular JavaScript library for building user interfaces.

Understanding Components​

Think of components as self-contained pieces of code that are responsible for one aspect of the user interface. They can be as simple as a button or as complex as a whole page. Components are combined together to build more complex UIs. Because components are reusable, they can help make your code more DRY (Don't Repeat Yourself).

Every component in Next.js is a JavaScript function that returns a React element. This React element describes how a section of the UI should appear.

For example, here's a simple component that returns a greeting message:

function Greeting() {
  return <h1>Hello, Next.js!</h1>;
}

In this example, Greeting is a component that returns a h1 React element.

Functional and Class Components​

There are two types of components in Next.js: functional components and class components.

Functional components are just JavaScript functions. They take in props as an argument and return a React element. Here's an example:

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

Class components are more complex. They're ES6 classes that extend React.Component. They must have a render method that returns a React element. Here's an example:

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

The choice between functional and class components often comes down to the specific needs of the component. However, with the introduction of hooks in React, most of the features exclusive to class components are now available in functional components. Therefore, functional components are generally preferred.

Using Components​

Components can be used inside other components. This allows you to build complex user interfaces out of simple building blocks. Here's an example:

function App() {
  return (
    <div>
      <Greeting />
      <Welcome name="Next.js" />
    </div>
  );
}

In this example, App is a component that uses the Greeting and Welcome components.

Props​

Props (short for properties) are how components talk to each other. They are inputs to a component and they can be of any type: numbers, strings, objects, arrays, functions, etc.

You can think of props as the arguments to a function. Just like how you pass arguments to a function, you pass props into a component.

Here's an example:

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

function App() {
  return <Welcome name="Next.js" />;
}

In this example, name is a prop that is passed from the App component to the Welcome component.

In conclusion, components are the building blocks of any Next.js application. They help you build complex user interfaces out of simple pieces. Understanding how to define and use components is essential for building applications with Next.js.