How to solve the window.ethereum / window undefined problem in Nextjs

ethers.ts

useEffect(() => {
    if (
      typeof window !== 'undefined' &&
      typeof window.ethereum !== 'undefined'
    ) {
      const provider = new ethers.providers.Web3Provider(
        window.ethereum as any
      );
      // @ts-ignore
      setSigner(provider.getSigner());
    }
  }, []);