What is the specific file where you can insert code that will apply to every page within the app directory of Next.js?

Question

What is the specific file where you can insert code that will apply to every page within the app directory of Next.js?

Where is the main global file to use useEffect for all pages? Previously in Next.js, you could utilize useEffect in _app.tsx, impacting all pages. Take a look at this example:

const MyApp = ({ Component, pageProps }: AppProps) => {
  useEffect(() => {
     console.log("Hello!")
   )}

  return (
    <>
      <Head>
        <title>Title</title>
      </Head>

    </>
  );
};

Previously, you would see the console.log on every page. With the new directory structure in Next.js using the app directory, where should you place the global useEffect? As server-side files like layout.tsx are not suitable for useEffect.

reactjs next.js

Answer 1

Answer №1

If you refer to the Upgrade Guide, you will see that instead of having separate files for pages/_app.js and pages/_document.js, they have been consolidated into a single root layout named app/layout.js.

This means that you can now place your useEffect in the app/layout.js file and turn it into a client-side component by adding "use client" at the top. Keep in mind that this setup does not restrict other parts of the application from being server components:

// app/layout.js

"use client";

export default function RootLayout({ children }) {
  
  useEffect(() => {
     console.log("Hello!")
  }, []);

  return (
    <html lang="en">
      <body>
        {children}
      </body>
    </html>
  );
}

If you prefer not to have your root layout as a client-side component, you can opt for an alternative approach using a different component like shown below:

// SomeGlobalComponent.js

"use client";

export default function SomeGlobalComponent() {
  useEffect(() => {
     console.log("Hello!")
  }, []);

  return <></>;
}

// app/layout.js

import SomeGlobalComponent from "./SomeGlobalComponent";

export default function RootLayout({ children }) {
  return (
    <html lang="en">
      <body>
        <SomeGlobalComponent />
        {children}
      </body>
    </html>
  );
}

Answer 2

If you refer to the Upgrade Guide, you will see that instead of having separate files for pages/_app.js and pages/_document.js, they have been consolidated into a single root layout named app/layout.js.

This means that you can now place your useEffect in the app/layout.js file and turn it into a client-side component by adding "use client" at the top. Keep in mind that this setup does not restrict other parts of the application from being server components:

// app/layout.js

"use client";

export default function RootLayout({ children }) {
  
  useEffect(() => {
     console.log("Hello!")
  }, []);

  return (
    <html lang="en">
      <body>
        {children}
      </body>
    </html>
  );
}

If you prefer not to have your root layout as a client-side component, you can opt for an alternative approach using a different component like shown below:

// SomeGlobalComponent.js

"use client";

export default function SomeGlobalComponent() {
  useEffect(() => {
     console.log("Hello!")
  }, []);

  return <></>;
}

// app/layout.js

import SomeGlobalComponent from "./SomeGlobalComponent";

export default function RootLayout({ children }) {
  return (
    <html lang="en">
      <body>
        <SomeGlobalComponent />
        {children}
      </body>
    </html>
  );
}

What is the specific file where you can insert code that will apply to every page within the app directory of Next.js?

Answer №1

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