Type Error: Type 'Element' is not assignable to type 'NextPage' – The Ultimate Guide

Are you tired of seeing that pesky error message “Type 'Element' is not assignable to type 'NextPage'”? Well, you’re in luck because today we’re going to dive deep into the world of Next.js and TypeScript to understand what’s causing this issue and how to fix it.

What is NextPage?

In Next.js, a `NextPage` is a type that represents a server-side rendered page. It’s a concept that Next.js uses to determine which pages should be rendered on the server and which should be rendered on the client.

// pages/index.tsx
import type { NextPage } from 'next';

const HomePage: NextPage = () => {
  return (
    <>
      <h1>Welcome to my homepage!</h1>
    <>
  );
};

export default HomePage;

In the example above, we’re defining a `HomePage` component that returns a simple `h1` element. The `NextPage` type is used to indicate that this component should be rendered on the server.

What is Element?

In React, an `Element` is a type that represents a virtual DOM element. It’s an object that describes a DOM element, its properties, and its children.

// components/MyComponent.tsx
import * as React from 'react';

const MyComponent: React.Element =<> {
  return (
    <>
      <p>Hello World!</p>
    <>
  );
};

In the example above, we’re defining a `MyComponent` component that returns a simple `p` element. The `React.Element` type is used to indicate that this component returns a virtual DOM element.

The Error: Type 'Element' is not assignable to type 'NextPage'

So, what happens when we try to assign an `Element` to a `NextPage`? Well, TypeScript gets angry and throws an error!

// pages/index.tsx
import type { NextPage } from 'next';
import { MyComponent } from '../components/MyComponent';

const HomePage: NextPage = MyComponent; // ERROR: Type 'Element' is not assignable to type 'NextPage'.

This error occurs because `NextPage` expects a function that returns a server-side rendered page, but `MyComponent` returns a virtual DOM element.

Why is this an Error?

The reason why this is an error is because `NextPage` and `Element` are fundamentally different types. `NextPage` represents a server-side rendered page, while `Element` represents a virtual DOM element.

If we were to assign an `Element` to a `NextPage`, Next.js would not know how to render the page on the server. It would try to render a virtual DOM element, which would result in a runtime error.

How to Fix the Error?

So, how do we fix this error? There are a few ways to do it, depending on your use case.

Option 1: Return a Function Component

If you want to return a server-side rendered page, you can return a function component that returns a JSX element.

// pages/index.tsx
import type { NextPage } from 'next';

const HomePage: NextPage = () => {
  return (
    <>
      <h1>Welcome to my homepage!</h1>
    <>
  );
};

In this example, we’re defining a `HomePage` component that returns a function that returns a JSX element. This is a valid `NextPage` because it returns a server-side rendered page.

Option 2: Use the `` Component

If you want to return a virtual DOM element, you can use the `` component from `next`.

// pages/index.tsx
import type { NextPage } from 'next';
import { MyComponent } from '../components/MyComponent';

const HomePage = () => {
  return (
    <NextPage>
      <MyComponent />
    </NextPage>
  );
};

In this example, we’re wrapping our `MyComponent` element with the `` component. This tells Next.js to render the page on the server.

Option 3: Create a Higher-Order Component

If you want to reuse your `MyComponent` component in multiple pages, you can create a higher-order component (HOC) that wraps it.

// components/withNextPage.tsx
import type { NextPage } from 'next';

const withNextPage = (WrappedComponent: React.Element) => {
  const WithNextPage: NextPage = () => {
    return <WrappedComponent />;
  };

  return WithNextPage;
};

// pages/index.tsx
import { withNextPage } from '../components/withNextPage';
import { MyComponent } from '../components/MyComponent';

const HomePage = withNextPage(MyComponent);

In this example, we’re creating a HOC that takes a virtual DOM element as an argument and returns a `NextPage` component that wraps it. We can then use this HOC to wrap our `MyComponent` component in multiple pages.

Conclusion

In conclusion, the error “Type 'Element' is not assignable to type 'NextPage'” occurs when we try to assign a virtual DOM element to a `NextPage` component. To fix this error, we can return a function component, use the `` component, or create a higher-order component that wraps our virtual DOM element.

By understanding the differences between `NextPage` and `Element`, we can write more robust and scalable code that takes advantage of Next.js’s server-side rendering capabilities.

Frequently Asked Questions

Q: What is the difference between `NextPage` and `Element`?

A: `NextPage` represents a server-side rendered page, while `Element` represents a virtual DOM element.

Q: Why can’t I assign an `Element` to a `NextPage`?

A: Because `NextPage` expects a function that returns a server-side rendered page, while `Element` returns a virtual DOM element.

Q: How do I fix the error “Type 'Element' is not assignable to type 'NextPage'”?

A: You can fix this error by returning a function component, using the `` component, or creating a higher-order component that wraps your virtual DOM element.

Solution	Description
Return a Function Component	Return a function component that returns a JSX element.
Use the `` Component	Wrap your virtual DOM element with the `` component.
Create a Higher-Order Component	Create a HOC that wraps your virtual DOM element and returns a `NextPage` component.

Resources

• Next.js Pages API
• React API
• TypeScript React Handbook

By following the instructions in this article, you should be able to fix the error “Type 'Element' is not assignable to type 'NextPage'” and create robust and scalable Next.js applications.

Final Thoughts

In conclusion, the error “Type 'Element' is not assignable to type 'NextPage'” is a common issue that occurs when working with Next.js and TypeScript. By understanding the differences between `NextPage` and `Element`, and using the solutions outlined in this article, you can create robust and scalable Next.js applications that take advantage of server-side rendering.

Remember, practice makes perfect, so go ahead and try out the solutions outlined in this article to see which one works best for your use case.

Happy coding!

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Frequently Asked Question

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I hope this helps!