In a Next.js project, you can declare the types for your variables, functions, and components using TypeScript or PropTypes.

To use TypeScript, you can install it as a dependency:

npm install --save-dev typescript @types/react @types/node

Then, create a tsconfig.json file in the root directory of your project:

    "lib": ["dom", "dom.iterable", "esnext"],

    "forceConsistentCasingInFileNames": true

  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],

This sets up TypeScript to compile your code and provides some configuration options.

To declare types for your components, you can use the React.FC (function component) type:

const MyComponent: React.FC<Props> = ({ name }) => {

You can also use interfaces to define the shape of an object:

Alternatively, you can use PropTypes to declare the expected types for your props:

Using PropTypes requires you to install it as a dependency:

Once you have declared your types, you can use them throughout your code to ensure type safety and catch errors at compile time.

For example, if you have a function that expects a certain type of argument, you can declare the type for that argument:

function addNumbers(a: number, b: number): number {

const result = addNumbers(2, '3'); // Type error: Argument of type 'string' is not assignable to parameter of type 'number'.

In this example, passing a string instead of a number as the second argument to addNumbers results in a type error.

Overall, declaring types can help improve the maintainability and reliability of your Next.js project.

There are two methods for declaration type in NextJS, so let's go to know what are the methods of type declaration in a NextJS project.

declaring-type-in-nextjs