Joodi

Posted on Jan 22

Understanding Template Files in Next.js 15: The Complete Guide

#nextjs #typescript #javascript #react

Next.js 15 introduces the template file, a sibling to layout, providing developers with fine-grained control over how their layouts behave during route transitions. This guide explores the differences between template and layout, their use cases, and best practices.

What is a Template File?

A template file in Next.js is used to define reusable layouts that reset their state or re-render when navigating between pages. This contrasts with layout, which maintains its state across route transitions.

Template vs. Layout

Feature	Layout	Template
State Persistence	Maintains state across route transitions.	Resets state on every route transition.
Reusability	Used for consistent layouts shared across multiple pages.	Similar to layout but ensures fresh rendering for every page.
When to Use	When you want components like headers, sidebars, or footers to persist across pages.	When you need layouts to reset or reinitialize for each route, such as forms or dynamic content.
Rendering Behavior	Does not re-render when navigating between sibling routes.	Re-renders every time the route changes.

When to Use Template vs. Layout

Use Template When:

You need to reset or reinitialize state during route transitions.
Forms or inputs within the layout require resetting their values.
Content is highly dynamic and needs to reflect route-specific changes.

Use Layout When:

You need a persistent structure, like a navigation bar or footer.
Components within the layout are static or don’t require frequent reinitialization.

Example: Input Resetting Behavior

Let’s look at an example to illustrate the difference between layout and template.

Using Layout (State Persists):

// app/layout.tsx
import './globals.css';

export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <body>
        <header>Header Content</header>
        <input placeholder="Type something..." />
        {children}
      </body>
    </html>
  );
}

In this example, if you type something into the input field and navigate to a different route, the input value will persist because the layout does not re-render.

Using Template (State Resets):

// app/template.tsx
import './globals.css';

export default function RootTemplate({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <body>
        <header>Header Content</header>
        <input placeholder="Type something..." />
        {children}
      </body>
    </html>
  );
}

Here, the input value resets every time you navigate to a new route, because the template file forces a re-render.

Dynamic Behavior with Template

A key advantage of using templates is their ability to handle dynamic content efficiently. For instance, in an e-commerce application, a template file can ensure that filters or search inputs reset when users navigate between product categories.

Example: Dynamic Product Filters

// app/shop/template.tsx
export default function ShopTemplate({ children }: { children: React.ReactNode }) {
  return (
    <main>
      <h1>Shop</h1>
      <input type="text" placeholder="Search products..." />
      {children}
    </main>
  );
}

With this setup, the search input resets every time the user navigates between categories, ensuring a fresh user experience.

Best Practices

1. Evaluate State Requirements

Use layout for persistent state (e.g., navigation or user authentication).
Use template for resetting state-sensitive components (e.g., forms, dynamic filters).

2. Avoid Overusing Templates

Templates are useful but can lead to unnecessary re-renders if used indiscriminately. Stick to layout for static or less-dynamic components.

3. Structure for Performance

Keep templates lightweight by avoiding heavy computations or large components.

4. Test Navigation Behavior

Ensure that your choice of layout or template aligns with the user experience, especially for interactive components like forms or modals.

Conclusion

Understanding the difference between layout and template in Next.js 15 is crucial for building efficient and user-friendly applications. While layout ensures persistence and stability, template offers flexibility for resetting state and dynamic re-renders. By leveraging these features effectively, you can create applications that are both performant and intuitive.

I hope you found this helpful! Let’s connect on LinkedIn or GitHub 🚀

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