Gatsby Browser API Error Fix

In this tutorial, you'll learn about Gatsby Browser API Error Fix. We cover key concepts, practical examples, and best practices.

The Problem

error "window" is not available during server-side rendering.

Using browser APIs like window, document, or localStorage in Gatsby components that render on the server.

Wrong

function Header() {
  const width = window.innerWidth
  return <h1>Width: {width}</h1>
}

Output: "window" is not available during server-side rendering.

window is undefined during the Node.js build process.

Right

Check for the browser environment:

import { useEffect, useState } from 'react'

function Header() {
  const [width, setWidth] = useState(0)

  useEffect(() => {
    setWidth(window.innerWidth)
  }, [])

  return <h1>Width: {width}</h1>
}

Or use gatsby-browser.js for browser-only code:

// gatsby-browser.js
export const onClientEntry = () => {
  window.addEventListener('resize', () => {})
}

Output: component renders safely on server with default value, then updates on client.

Prevention

• Wrap browser API calls in useEffect or componentDidMount
• Use Gatsby Browser APIs (gatsby-browser.js) for browser-only code
• Check for typeof window !== 'undefined' before accessing browser objects

Common Mistakes with browser api

1. Using foldl instead of foldl' causing stack overflow on large lists
2. Forgetting deriving (Show, Eq) on custom data types needed for debugging
3. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable

These mistakes appear frequently in real-world GATSBY code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ