How to Fix Typeerror in Next.js When Deploying

Resolving TypeError in Next.js When Deploying

Next.js TypeErrors during deployment commonly stem from server/client code boundary issues, missing environment variables, or API responses that differ between environments.

Why It Happens at Deploy Time

• window or document accessed in server-rendered code
• Environment variables available locally but not configured in production
• API responses returning different shapes than expected

The Fix

Guard environment-specific code and validate data:

// lib/config.ts
function getConfig() {
  const apiUrl = process.env.NEXT_PUBLIC_API_URL;
  if (!apiUrl) {
    throw new TypeError(
      'NEXT_PUBLIC_API_URL is not defined. Check your .env file.'
    );
  }
  return { apiUrl };
}

// components/Chart.tsx - client-only component
import dynamic from 'next/dynamic';

const Chart = dynamic(() => import('./ChartInner'), {
  ssr: false,
  loading: () => <div>Loading chart...</div>,
});

// lib/api.ts - validate API responses
interface User { id: number; name: string; }

function isUser(data: unknown): data is User {
  return (
    typeof data === 'object' && data !== null &&
    'id' in data && 'name' in data
  );
}

Use dynamic imports with ssr: false for browser-only libraries, and validate all external data shapes.

Bugsly for Next.js Deployments

Bugsly distinguishes between server-side and client-side errors in Next.js, showing you exactly which rendering phase triggered the TypeError and what data was involved.