Master TypeScript in React: 5 JavaScript to TypeScript Examples

TypeScript is a statically typed, object-oriented programming language that is built on JavaScript. It adds type annotations and other features to the JavaScript language, making it easier to write and maintain large codebases. React JS is a JavaScript library for building user interfaces.

In this tutorial, we’ll discuss the following topics:

1. Advantages of using TypeScript in React JS applications
2. Setting up a React JS project with TypeScript
3. 5 examples of how to write TypeScript code in React JS
4. Common problems and precautions to keep in mind while using TypeScript in React JS
5. Better ways to use third-party packages in a TypeScript-React JS project

Advantages of using TypeScript in React JS Applications:

1. Improved code quality: TypeScript provides type annotations and other features that help catch errors early in the development process.
2. Better maintainability: TypeScript makes it easier to understand and maintain large codebases by providing clear type information for variables, functions, and other constructs.
3. Improved developer productivity: TypeScript’s features can save time and reduce frustration for developers by catching errors before they become bugs.

Setting up a React JS Project with TypeScript:

1. Install Node.js and npm on your computer
2. Use the npm init command to create a new package.json file
3. Use npm install command to install the required dependencies
4. Use the npm run build command to compile the TypeScript code
5. Use the npm start command to run the development server and start the application

5 Examples of How to Write TypeScript Code in React JS:

Unlock the Power of TypeScript in Your React Apps! Join us as we show you how to effortlessly transform your JavaScript code snippets with these in-demand use cases

1. Defining props types in a functional component
2. Using interfaces to define state types in a class component
3. Creating type-safe custom hooks
4. Using generics to type functions that return JSX elements
5. Creating type-safe utility functions for your React components

1. Defining props types in a functional component

Defining prop types in a functional component is a way to specify the type of the props that the component should receive. This helps to catch bugs and improve code maintainability by catching mistakes early in the development process. In TypeScript, prop types can be defined using an interface or a type. Here’s how it can be done in a functional component:

JavaScript:

import React from 'react';

const ExampleComponent = (props) => {
  return (
    <div>
      <h1>Hello, {props.name}!</h1>
      <p>{props.message}</p>
    </div>
  );
};

export default ExampleComponent;

TypeScript:

import React from 'react';

interface Props {
  name: string;
  message: string;
}

const ExampleComponent: React.FC<Props> = (props) => {
  return (
    <div>
      <h1>Hello, {props.name}!</h1>
      <p>{props.message}</p>
    </div>
  );
};

export default ExampleComponent;

As you can see, the TypeScript version of the code includes an interface Props that defines the shape of the props object passed to the component. This allows TypeScript to catch any errors if the component is used with props that don’t match the expected shape. The React.FC type is used to declare the type of the component.

2. Using interfaces to define state types in a class component

Guide to using TypeScript in React class components to declare and enforce the types of state data. Interfaces provide a way to describe the structure of an object and its properties, making it possible to catch bugs and ensure code consistency and maintainability. By defining the state data structure in an interface, developers can catch type-related errors at compile-time, rather than having to debug them at runtime. This guide will walk you through the process of defining an interface for state data and using it in a class component, providing a practical example and best practices along the way.

JavaScript:

import React, { useState } from 'react';

const ExampleComponent = () => {
  const [count, setCount] = useState(0);

  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
};

export default ExampleComponent;

TypeScript:

import React, { useState } from 'react';

const ExampleComponent = () => {
  const [count, setCount] = useState<number>(0);

  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
};

export default ExampleComponent;

In this example, the type of the count state variable is explicitly set to number in the TypeScript version. This provides better type safety and makes it easier to catch bugs related to incorrect state usage.

3. Creating type-safe custom hooks

It’s important to create custom hooks that are type-safe. This means that the custom hook should be written in a way that allows for proper type checking, making it easier to catch bugs and improve code maintainability. By creating type-safe custom hooks, you can ensure that your code is more robust and less prone to errors, making it easier to maintain and scale over time. In this section, you will learn how to create custom hooks that are type-safe, making it easier to write high-quality, maintainable code in your TypeScript React app.

JavaScript:

import React, { useState, useEffect } from 'react';

const useFetchData = (url) => {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetch(url)
      .then((response) => response.json())
      .then((json) => setData(json));
  }, [url]);

  return data;
};

const ExampleComponent = () => {
  const data = useFetchData('https://jsonplaceholder.typicode.com/posts');

  return (
    <div>
      {data ? (
        <ul>
          {data.map((item) => (
            <li key={item.id}>{item.title}</li>
          ))}
        </ul>
      ) : (
        <p>Loading...</p>
      )}
    </div>
  );
};

export default ExampleComponent;

TypeScript:

import React, { useState, useEffect } from "react";

interface Data {
  id: number;
  title: string;
  body: string;
}

const useFetchData = (url: string): Data[] | null => {
  const [data, setData] = useState<Data[] | null>(null);

  useEffect(() => {
    fetch(url)
      .then((response) => response.json())
      .then((json) => setData(json));
  }, [url]);

  return data;
};

const ExampleComponent = () => {
  const data = useFetchData("https://jsonplaceholder.typicode.com/posts");

  return (
    <div>
      {data ? (
        <ul>
          {data.map((item) => (
            <li key={item.id}>{item.title}</li>
          ))}
        </ul>
      ) : (
        <p>Loading...</p>
      )}
    </div>
  );
};

export default ExampleComponent;

4. Using generics to type functions that return JSX elements

The use of generics in TypeScript allows for typing functions that return JSX elements. This helps in ensuring that the returned elements are of the correct type and catch any errors early in the development process. When converting from JavaScript to TypeScript, using generics to type functions that return JSX elements is a good practice to adopt as it helps improve the overall quality and maintainability of the code.

JavaScript:

import React, { useState } from 'react';

const ExampleComponent = () => {
  const [inputValue, setInputValue] = useState('');

  const handleInputChange = (event) => {
    setInputValue(event.target.value);
  };

  return (
    <div>
      <input type="text" onChange={handleInputChange} value={inputValue} />
      <p>Input value: {inputValue}</p>
    </div>
  );
};

export default ExampleComponent;

TypeScript:

import React, { useState } from 'react';

const ExampleComponent = () => {
  const [inputValue, setInputValue] = useState('');

  const handleInputChange = (event: React.ChangeEvent<HTMLInputElement>) => {
    setInputValue(event.target.value);
  };

  return (
    <div>
      <input type="text" onChange={handleInputChange} value={inputValue} />
      <p>Input value: {inputValue}</p>
    </div>
  );
};

export default ExampleComponent;

The React.ChangeEvent type is used to declare the type of the event parameter in the handleInputChange function. This provides better type safety and makes it easier to catch bugs related to incorrect event handling.

5. Creating type-safe utility functions for your React components

This example refers to the process of converting utility functions in a React application from JavaScript to TypeScript, with a focus on ensuring type safety. This means that the code uses TypeScript’s type system to specify the data types of parameters and return values, which helps to catch bugs and improve code maintainability. By converting utility functions to TypeScript, developers can ensure that the code is more robust and less prone to errors, making it easier to maintain and scale over time. This can be a key step in converting a React application from JavaScript to TypeScript and improving its overall quality.

JavaScript:

import React from 'react';

const ExampleComponent = (props) => {
  return (
    <div>
      <h1>Hello, {props.name}!</h1>
      <p>{props.message}</p>
    </div>
  );
};

ExampleComponent.defaultProps = {
  name: 'Stranger',
  message: 'Welcome to React!',
};

export default ExampleComponent;

TypeScript:

import React from 'react';

interface Props {
  name: string;
  message: string;
}

const ExampleComponent: React.FC<Props> = ({ name, message }) => {
  return (
    <div>
      <h1>Hello, {name}!</h1>
      <p>{message}</p>
    </div>
  );
};

ExampleComponent.defaultProps = {
  name: 'Stranger',
  message: 'Welcome to React!',
};

export default ExampleComponent;

The Props interface is used to declare the expected shape of the props object passed to the component. This provides better type safety and makes it easier to catch bugs related to incorrect prop usage. Additionally, destructuring is used in the component implementation to extract the name and message props from the props object.

Common Problems and Precautions to Keep in Mind While Using TypeScript in React JS:

1. Be careful when using any, especially when dealing with third-party libraries.
2. Pay close attention to type inference when defining variables.
3. Be careful when using type assertions.
4. Keep your types up-to-date as your code evolves.

Better Ways to Use Third-Party Packages in a TypeScript-React JS Project:

1. Use @types packages from DefinitelyTyped to get type definitions for popular JavaScript libraries.
2. Make sure to check the types of the objects returned by third-party functions before using them.
3. Consider using a type checker like TypeScript to validate the types of objects returned by third-party functions.

Conclusion

In conclusion, using TypeScript in React JS applications can improve code quality, maintainability, and developer productivity. With the right setup and knowledge of its features, you can write high-quality, type-safe code with React and TypeScript.