How to Declare Constants in React Class?

When developing applications with React, it's necessary to declare constants to store values that remain unchanged throughout the lifecycle of a component or application. Constants can help improve code readability, provide a central location for managing shared values, and enhance maintainability. In this article, we'll explore how to declare constants in a React class component.

Importing React

To begin, let's assume you have set up your React environment and have a class component ready for use. Before declaring constants, make sure you have imported the necessary libraries. This includes importing React, which is the core library for building user interfaces in React.

import React from 'react';

Declaring Constants in a React Class Component

To declare constants in a React class component, you have two options:

• Static class properties:Static class properties are declared directly inside the class definition and can be accessed without creating an instance of the class. This approach allows you to define constants that are shared among all instances of the component.

Example

In the example below, we declare a constant named MY_CONSTANT within the class constructor. The constant is then accessed within the render method using this.MY_CONSTANT.

class MyComponent extends React.Component {
  static MY_CONSTANT = 'Hello, World!';

  render() {
    return <div>{MyComponent.MY_CONSTANT}</div>;
  }
}

Output

Hello, World!

• Class−level variables:Class−level variables can be declared inside the class constructor. Unlike static class properties, class−level variables are specific to each instance of the component. This approach is useful when you need instance−specific constants.

Example

In the example below, we declare a constant named MY_CONSTANT within the class constructor. The constant is then accessed within the render method using this.MY_CONSTANT.

class MyComponent extends React.Component {
  constructor(props) {
    super(props);

    this.MY_CONSTANT = 'Hello, World!';
  }

  render() {
    return <div>{this.MY_CONSTANT}</div>;
  }
}

Output

Hello, World!

Using Constants in React Components

Once you have declared constants in your React class component, you can use them within your component's methods, lifecycle hooks, or JSX templates. Let's see how to utilize the declared constants in the following example:

Example

In the below example, the constant MY_CONSTANT is accessed within the handleClick method, which is triggered when the button is clicked. The constant is also rendered within the <p> tag in the JSX template.

class MyComponent extends React.Component {
  static MY_CONSTANT = 'Hello, World!';

  handleClick() {
    console.log(MyComponent.MY_CONSTANT);
  }

  render() {
    return (
      <div>
        <button onClick={this.handleClick}>Click Me</button>
        <p>{MyComponent.MY_CONSTANT}</p>
      </div>
    );
  }
}

Output

Conclusion

In this article, we discussed how we can declare constants in react class. Declaring constants in React class components provides a way to store values that remain unchanged throughout the component's lifecycle. Whether using static class properties or class−level variables, constants enhance code readability, and maintainability, and provide a central location for managing shared values