đŸ¶
Next.js

Fix "window is not defined" Error in Next.js App

By Filip on 04/20/2024

Learn how to fix the "window is not defined" error in Next.js, a common issue caused by server-side rendering and the use of window object methods within components.

Fix "window is not defined" Error in Next.js App

Table of Contents

Introduction

The "window is not defined" error is a common challenge faced by Next.js developers due to the framework's server-side rendering (SSR) capabilities. This guide will provide a step-by-step approach to understanding and resolving this issue, ensuring your Next.js applications function seamlessly.

Step-by-Step Guide

The "window is not defined" error is a common hurdle in Next.js development, often arising from the framework's server-side rendering (SSR) capabilities. Here's a step-by-step approach to understand and resolve this issue:

Understanding the Root Cause:

  1. Server-Side Rendering (SSR): Next.js renders pages on the server before sending them to the client. The server environment lacks browser-specific globals like window and document, leading to the error when code tries to access them during SSR.

Solutions:

1. Conditional Rendering with useEffect and useState:

  • Scenario: You need to access window properties or browser APIs after the component mounts in the browser.
  • Steps:
    1. Import useEffect and useState:
    import { useEffect, useState } from 'react';
    1. Create a state variable to store window-dependent data:
    const [windowWidth, setWindowWidth] = useState(null);
    1. Use useEffect to access window properties and update the state after the component mounts:
    useEffect(() => {
    if (typeof window !== 'undefined') {
        setWindowWidth(window.innerWidth);
    }
}, []);
    1. Use the state variable in your component's JSX:
    return <div>Window width: {windowWidth}</div>;

2. Dynamic Imports with next/dynamic:

  • Scenario: You have a component that heavily relies on browser APIs and needs to be completely client-side rendered.
  • Steps:
    1. Import next/dynamic:
    import dynamic from 'next/dynamic';
    1. Wrap the component with dynamic and set ssr to false:
    const MyClientSideComponent = dynamic(() => import('./MyComponent'), { ssr: false });
    1. Use the dynamically imported component in your page or other components:
    <MyClientSideComponent />

3. Opting Out of SSR with getServerSideProps or getStaticProps:

  • Scenario: You have an entire page that relies heavily on browser APIs and doesn't benefit from SSR.
  • Steps:
    1. Define getServerSideProps or getStaticProps in your page component:
    export async function getServerSideProps(context) {
    // ... any server-side logic ...
    return { props: {} };
}
    1. This prevents the page from being pre-rendered on the server, avoiding the "window is not defined" error.

Additional Tips:

  • Use libraries like isomorphic-unfetch for fetching data that works on both server and client.
  • Consider using a custom server if you need more control over the rendering process.
  • Always test your application in both development and production environments to ensure proper behavior.

By understanding the cause of the "window is not defined" error and applying these solutions, you can effectively build Next.js applications that leverage both server-side rendering and client-side interactivity.

Code Example

This code provides solutions for the "Window is not defined" error in Next.js, a common issue when using browser-specific APIs on the server-side. It presents three methods:

  1. Conditional Rendering: Uses useEffect and useState to check if window is defined and update the state accordingly, ensuring browser-specific code runs only on the client-side.

  2. Dynamic Imports: Leverages next/dynamic to dynamically import components that rely on window or document, preventing them from being rendered on the server.

  3. Opting Out of SSR: Employs getServerSideProps or getStaticProps to bypass server-side rendering for pages that require browser-specific APIs.

Additionally, it demonstrates using isomorphic-unfetch for data fetching that works seamlessly on both server and client.

Following your provided explanations, here are the JavaScript examples for each solution:

1. Conditional Rendering with useEffect and useState:

import { useEffect, useState } from 'react';

function MyComponent() {
  const [windowWidth, setWindowWidth] = useState(null);

  useEffect(() => {
    // Check if window is defined (client-side)
    if (typeof window !== 'undefined') {
      setWindowWidth(window.innerWidth); // Update state with window width
    }
  }, []); // Empty dependency array ensures it runs only once on mount

  return (
    <div>
      Window width: {windowWidth}
    </div>
  );
}

export default MyComponent;

2. Dynamic Imports with next/dynamic:

import dynamic from 'next/dynamic';

// Client-side component (assumes it uses window or document)
const MyClientSideComponent = dynamic(
  () => import('./MyComponent'), // Replace with your component path
  { ssr: false } // Disable server-side rendering
);

function MyPage() {
  return (
    <div>
      {/* This component will only load on the client-side */}
      <MyClientSideComponent />
    </div>
  );
}

export default MyPage;

3. Opting Out of SSR with getServerSideProps or getStaticProps:

function MyPage(props) {
  // ... your component logic ...
}

// This page will not be pre-rendered on the server
export async function getServerSideProps(context) {
  // ... any server-side logic ...

  return {
    props: {}, // Pass any props needed by the component
  };
}

export default MyPage;

Additional Tips:

  • Fetching Data:
import fetch from 'isomorphic-unfetch';

// Works on both server and client
const fetchData = async () => {
  const response = await fetch('https://api.example.com/data');
  const data = await response.json();
  return data;
};

Remember to adapt these examples to your specific use case and component structure.

Additional Notes

Error Variations:

  • While the focus is on "window is not defined," similar errors can occur with other browser-specific globals like document, navigator, or localStorage. The solutions discussed apply to these cases as well.

SSR and SEO Benefits:

  • It's important to understand that SSR offers significant SEO advantages. Search engines can easily crawl and index SSR-rendered pages, improving your website's visibility.

Choosing the Right Solution:

  • The choice between the solutions depends on the specific use case and the extent to which a component relies on browser APIs.
    • For minor interactions, conditional rendering with useEffect is often sufficient.
    • For components heavily dependent on browser features, dynamic imports or opting out of SSR might be necessary.

Hydration Mismatch:

  • Be cautious when using client-side rendered content within SSR pages. Mismatches between the server-rendered HTML and the client-side generated content can lead to hydration errors. Ensure consistency to avoid unexpected behavior.

Testing and Debugging:

  • Thoroughly test your application in different environments (development, production) to catch any potential issues related to window or other browser globals.
  • Utilize browser developer tools to inspect component behavior and identify the source of errors.

Community and Resources:

  • The Next.js community is active and helpful. Refer to the official documentation, community forums, and online resources for further guidance and troubleshooting.

Beyond the Basics:

  • Explore advanced techniques like code-splitting and server components for more granular control over rendering and optimization.

Remember, the key is to strike a balance between leveraging SSR for SEO and performance while handling browser-specific code appropriately to avoid the "window is not defined" error.

Summary

Scenario Solution Explanation
Need to access window after component mounts Conditional rendering with useEffect and useState 1. Create state variable for window data. 2. Use useEffect to update state after mount. 3. Use state variable in JSX.
Component relies heavily on browser APIs Dynamic imports with next/dynamic 1. Wrap component with dynamic and set ssr to false. 2. Use the dynamically imported component.
Entire page relies on browser APIs Opt-out of SSR with getServerSideProps or getStaticProps Define these functions in your page component to prevent server-side rendering.

Conclusion

In conclusion, mastering the "window is not defined" error in Next.js is crucial for building robust and efficient web applications. By understanding the underlying causes and implementing the appropriate solutions, developers can harness the power of server-side rendering while ensuring seamless client-side interactions. Whether through conditional rendering, dynamic imports, or opting out of SSR, there's a strategy to address every scenario. Remember to carefully consider the trade-offs and choose the approach that best aligns with your project's requirements. With these insights and techniques, you'll be well-equipped to navigate the complexities of Next.js development and deliver exceptional user experiences.

References

Were You Able to Follow the Instructions?

😍Love it!
😊Yes
😐Meh-gical
😞No
đŸ€źClickbait

Related posts

React Constructor vs getInitialState: Key Differences

This article explores the key differences between using constructors and getInitialState in React and React Native for initializing state in your components, helping you choose the best approach for your project.

React children prop: array or element?

This article explores the type of the `children` prop in React, delving into its versatility and how it enables rendering various data types within components.

Multiple Arrow Functions in JavaScript

This article explains the meaning and usage of multiple arrow functions in JavaScript, including nested arrow functions and arrow function expressions within other functions.