React

Top 5 MUST KNOW Things in React, Examples, Meanings

Posted on Thursday, December 22, 2022
MUST KNOW Things in React

There is a lot of MUST KNOW things in React, but which ones should you focus the most, take a close look a out top 5 list included examples and meanings.

Table Of Contents
  1. Components: React is based on the concept of components, which are reusable pieces of code that represent a part of a user interface. Components can be thought of as building blocks that can be combined to create a complete application.
  2. JSX: JSX is a syntax extension for JavaScript that allows you to write HTML-like code in your React components. It makes it easier to create and manipulate the elements of a user interface, and it is a key aspect of the React way of building applications.
  3. State: React components have a state, which is an object that holds data that can be used to render the component. The state can be modified by events or user actions, and changes to the state can trigger the component to re-render.
  4. Props: Props are properties that are passed to a component from its parent. They are used to pass data and behavior down the component tree, and they can be used to customize the appearance and behavior of a component.
  5. Lifecycle methods: React components have a lifecycle, which is a set of methods that are called at different stages of the component’s life. These methods can be used to perform actions when a component is created, updated, or destroyed, and they are an important tool for managing the behavior of a component.

React Components: Explanation

In the React JavaScript library for building user interfaces, a component is a reusable piece of code that represents a part of a user interface. Components are typically used to encapsulate UI elements and their logic, and can be composed to create more complex UI elements.

There are two types of components in React: functional components and class-based components.

Functional components are simple JavaScript functions that accept props (short for “properties”) as arguments and return a React element. They are typically used for presentational components, which are responsible for rendering UI elements but do not have their own state. Here is an example of a functional component in React:

Copy codeimport React from 'react';

const MyButton = (props) => {
  return (
    <button>{props.label}</button>
  );
};

export default MyButton;

Class-based components are defined using JavaScript classes and are more powerful than functional components, as they can have their own state and lifecycle methods. They are typically used for container components, which are responsible for managing data and behavior. Here is an example of a class-based component in React:

Copy codeimport React from 'react';

class MyForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      name: '',
      email: '',
    };
  }

  handleChange = (event) => {
    this.setState({
      [event.target.name]: event.target.value,
    });
  };

  handleSubmit = (event) => {
    event.preventDefault();
    // submit form data
  };

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" name="name" value={this.state.name} onChange={this.handleChange} />
        </label>
        <br />
        <label>
          Email:
          <input type="email" name="email" value={this.state.email} onChange={this.handleChange} />
        </label>
        <br />
        <button type="submit">Submit</button>
      </form>
    );
  }
}

export default MyForm;

React components can be composed to create more complex UI elements by nesting them inside each other. For example, a component that represents a form might contain several components that represent individual form fields.

In addition to functional and class-based components, React also has special types of components called “hooks,” which allow developers to use state and other React features in functional components. Hooks are a way to reuse stateful logic across components without the need to create a class-based component.

JSX: Explanation

JSX is a syntax extension for JavaScript that allows you to write HTML-like code in your React components. It is a way of embedding HTML elements and attributes within JavaScript code, and it is used to define the structure and content of a user interface in React.

Here is an example of how you might use JSX to define a simple button component:

Copy codeimport React from 'react';

function Button(props) {
  return (
    <button style={props.style} onClick={props.onClick}>
      {props.children}
    </button>
  );
}

export default Button;

In this example, the JSX code creates a button element and sets its style and onClick attributes based on the props object passed to the component. The {props.children} expression is used to include the content of the button (e.g., the text “Click me”) in the JSX code.

JSX is not natively supported by JavaScript, so it needs to be transformed into regular JavaScript code before it can be executed in a browser. This transformation is typically done using a build tool like Babel.

JSX is an important part of the React ecosystem and is used extensively in the development of React applications. It allows developers to write declarative and concise code for building user interfaces, and it makes it easier to create and manipulate the elements of a user interface in a consistent and predictable way.

State: Explanation

In React, a component’s state is an object that stores values that determine a component’s behavior. The state can be modified by a component’s functions, and it triggers a re-render of the component when it changes.

Here is an example of a simple component with a state in React:

Copy codeclass MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  render() {
    return (
      <div>
        <p>You clicked {this.state.count} times</p>
        <button onClick={() => this.setState({ count: this.state.count + 1 })}>
          Click me
        </button>
      </div>
    );
  }
}

In this example, the component’s state is an object with a single property called “count”, which is initialized to 0. The component renders a button and a paragraph element that displays the current value of the “count” state. The button has an onClick event handler that increments the value of the “count” state by 1 every time the button is clicked.

When the component’s state changes, the component re-renders to reflect the new state. In this case, every time the button is clicked, the component’s render() function is called again, and the new value of the “count” state is displayed in the paragraph element.

It’s important to note that the component’s state should only be used for values that change within the component itself. For values that are passed to the component from its parent as props, it’s better to use props instead of state. This is because props are meant to be passed down from a parent component, whereas state is meant to store values that are specific to a particular component.

Props: Explanation

In the React JavaScript library for building user interfaces, props (short for “properties”) are a way to pass data from a parent component to a child component. Props are used to customize a component and make it more flexible and reusable.

Props are passed to a component as an object, and the component can access the props using the props object. Here is an example of a functional component that uses props:

Copy codeimport React from 'react';

const MyButton = (props) => {
  return (
    <button>{props.label}</button>
  );
};

export default MyButton;

In this example, the MyButton component accepts a label prop, which is used to set the text displayed on the button. The component can be used like this:

Copy codeimport MyButton from './MyButton';

<MyButton label="Click me" />

Props can be used to pass any type of data, including strings, numbers, booleans, arrays, and objects. They can also be used to pass functions, which can be used to handle events or perform other actions.

It’s important to note that props are read-only, which means that a component cannot modify its own props. If a component needs to modify data, it should use its own state or store the data in a higher-level component.

Props are a powerful tool for building flexible and reusable components in React, and are an important concept to understand when working with the library.

Lifecycle Method: Explanation

In React, a component goes through a lifecycle of events as it is created, rendered, and destroyed. These events are represented by lifecycle methods, which are functions that are called at specific points in a component’s lifecycle.

Here is a list of the main lifecycle methods in React:

  • constructor(): This method is called before a component is mounted (inserted into the DOM). It is used to initialize the component’s state and bind event handlers to the component’s instance.
  • componentDidMount(): This method is called after a component is mounted. It is used to trigger side effects, such as fetching data or interacting with the DOM.
  • shouldComponentUpdate(): This method is called before a component is re-rendered in response to a state or prop change. It allows the component to decide whether or not it should update by returning a boolean value. If the method returns true, the component will update; if it returns false, the component will not update.
  • componentDidUpdate(): This method is called after a component updates (re-renders). It is used to trigger side effects, such as interacting with the DOM or making network requests.
  • componentWillUnmount(): This method is called before a component is unmounted (removed from the DOM). It is used to clean up any resources or subscriptions that the component may have.

Here is an example of a simple component that uses some of these lifecycle methods:

Copy codeclass MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: null
    };
  }

  componentDidMount() {
    fetch('https://my-api.com/data')
      .then(response => response.json())
      .then(data => this.setState({ data }));
  }

  shouldComponentUpdate(nextProps, nextState) {
    return nextState.data !== this.state.data;
  }

  componentWillUnmount() {
    console.log('Component unmounting...');
  }

  render() {
    return (
      <div>
        {this.state.data ? <p>{this.state.data}</p> : <p>Loading...</p>}
      </div>
    );
  }
}

In this example, the constructor() method is used to initialize the component’s state with a data property, which is set to null. The componentDidMount() method is used to fetch data from an API and update the data state when the data is received. The shouldComponentUpdate() method is used to optimize the component by only allowing it to update when the data state changes. The componentWillUnmount() method is used to log a message to the console when the component is unmounted.

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