How to fix custom code optimization errors like “Cannot Set Property of Undefined”

Why optimization issues occur

Framer pre-renders pages on the server to improve performance and ensure compatibility across all devices. However, during pre-rendering:

• Browser-specific APIs like window, document, and navigator are not available because the server lacks browser context (e.g., browser settings, window size, cookies).

• Custom code that relies on these APIs will cause errors during pre-rendering.

Avoid browser-specific APIs

Write JavaScript that doesn’t rely on browser APIs for rendering.

• Instead of: Using window.innerWidth.

• Use: CSS media queries to handle layout changes based on screen size.

For example:

// ❌️ Bad: will cause optimization issues
export function Component() {
  const windowWidth = window.innerWidth

  return windowWidth < 768 ? <MobileVideo /> : <DesktopVideo />
}

// ✅ Good: won’t cause optimization issues
import { withCSS } from "framer"

function Component() {
  return <>
    <style>{`
      .my-component-video-mobile { display: block }
      .my-component-video-desktop { display: none }
        
      @media (min-width: 768px) {
        .my-component-video-mobile { display: none }
        .my-component-video-desktop { display: block }
      }
    `}</style>
    <div className="my-component-video-mobile"><MobileVideo /></div>
    <div className="my-component-video-desktop"><DesktopVideo /></div>
  </>
}

Put browser-specific API calls into useEffect

If you can’t avoid using browser-specific APIs, try moving them inside useEffect instead. useEffect executes only in the browser, when the page has fully loaded, so it won’t cause optimization issues. For example:

// ❌️ Bad: will cause optimization issues
function Component() {
  window.gtag("event", "component_rendered")

  return <div>Hello!</div>
}

// ✅ Good: won’t cause optimization issues
function Component() {
  useEffect(() => {
    window.gtag("event", "component_rendered")
  }, [])

  return <div>Hello!</div>
}

Use placeholders for browser-dependent data

If your component needs information like document.cookie (e.g., user login status) or navigator.language:

1. Write a component that shows a placeholder during pre-rendering.

2. After the page loads, update the component with the correct data.

Example: framer-optim-1.jsx

Opt out of optimization

If necessary, you can opt your component out of optimization entirely:

1. Skip pre-rendering for the component using server-side logic.

2. Note:

   • The component’s content won’t be accessible to search engines.

   • It will only load after the page has fully loaded.

   • Use a placeholder to provide a fallback experience for better usability.

Example: framer-optim-2.jsx

Apply the same approach to overrides

For custom overrides:

• Use placeholders or opt out of optimization in a similar way to components.

Example: framer-optim-3.jsx

If you're still experiencing issues, please reach out to us through our contact page for further help or check out the Developer Space.

Example: framer-optim-3.jsx

If you're still experiencing issues, please reach out to us through our contact page for further help or check out the Developer Space.