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First app with NextJs 13: setup, the new /app folder, and routing system

NextJs 13 comes with a great set of new features. One of the major additions is the new /app folder as the root folder for the pages of our app. This determines also changes to the NextJs routing conventions.

The plan for this article is to build a simple store app with the following URL structure:

/              -> points to a basic static Index page
/products      -> points to a basic root static Products page
/products/_id_ -> points to a parameterized product page
/about         -> points to a static About page

In this article we will cover the following:

  • setting up a NextJs 13 project from scratch
  • using the /app folder to serve static pages
  • using query params in NextJs 13

Let's start learning!

Setting up a NextJs 13 project from scratch

Before we start the actual coding will need to set up the project.

Will start from scratch by creating an empty folder namednext13-jscraft-first. Inside this folder will first run the npm init command to create the package.json file with the default values:

npm init -y

Next, we will need to install the minimum required dependencies:

npm install next@latest react@latest react-dom@latest eslint-config-next@latest 

Given that NextJs 13 is still experimental will need to create a next.config.js file in the root of the out project with the following content:

/**
 * @type {import('next').NextConfig}
 */
module.exports = {
    experimental:{
        appDir: true
    }
}

Finally, open the package.json and in the scripts section add the below lines:

"build": "next build",
"start": "next start",
"dev": "next"

Using the /app folder to serve static pages

Before, we can see the first page of our new NextJs 13 project will need to create the /app folder at the root of our project.

The /app folder comes as a replacement for the /pages folder. For the moment, we can still use both of them so that we can have a smother upgrade to NextJs 13.

To define the main index page of our store app we will add a /app/page.js file.

At this point, our app should have the following files and folders:

/node_modules
/app
    page.js
next.config.js
package.json

In NextJs 13 page.js is a reserved filename and maps to the default entry page of a folder. Now, we can put other things in a subfolder of /app, not just javascript pages. We can add styles, subcomponents, or tests. NextJs needs this reserved page.js name to know what file to load first from a given folder.

For our /app/page.js we will just add a simple heading:

/* /app/page.js */
export default function Index() {
    return (
        <h1>šŸ” The Home Page</h1>
    )
}

With all of this in place, if we now run npm run dev we will see the below page up and running at http://localhost:3000/:

When we first run npm run dev you will see that two new items were added to our project folder:

  • a new autogenerated app/layout.js file. As the name implies it contains the layout description for our app. It replaces /pages/_app.js and /pages/_document.js files from the older versions of NextJs
  • the .next folder contains the build files (this was also present in the older Nexjs versions)

In order to add a second page to our app we will create a new folder app/about. We will need an entry point for this folder, meaning that we will need to add a page.js file. The content of app/about/page.js will be:

/* /app/about/page.js  */
export default function Index() {
    return (
        <h1>šŸ” The About page</h1>
    )
}

Now, if we visit http://localhost:3000/about we will see the newly created page:

Using query params in NextJs 13

So far, so good! But we have just used plain old static pages. What if we want to have URLs with the following format:

http://localhost:3000/products/1
http://localhost:3000/products/2
....
http://localhost:3000/products/1000

In order to add a query param to a route the convention is to create a new folder and wrap that query param name in square brackets.

We will name our query param id. So, we will create a new subfolder of /app called /products. And inside of /app/products, we will add a [id] subfolder containing the page.js file:

/* /app/products/[id]/page.js */
export default function ProductWithId({ params }) {
return (<h1>šŸ“¦ Individual product with id: {params.id} </h1>
}

Having this new page if we visit an URL like http://localhost:3000/products/123 we will see this output:

Keep in mind that we can still add a page.js in the root of our app/products folder:

/* /app/products/page.js */
export default function ProductIndex() {
    return (
        <h1>šŸ›’ Products Page</h1>
    )
}

And it will be accessible at the root of http://localhost:3000/products:

If you need to create links between these pages you can still use the Link component as before Next 13.

You can see the full code here

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