# Pages

In Next.js, a **page** is a [React Component](https://reactjs.org/docs/components-and-props.html) exported from a `.js`, `.jsx`, `.ts`, or `.tsx` file in the `pages` directory. Each page is associated with a route based on its file name.

**Example**: If you create `pages/about.js` that exports a React component like below, it will be accessible at `/about`.

```javascript
function About() {
  return <div>About</div>
}

export default About
```

#### Pages with Dynamic Routes

Next.js supports pages with dynamic routes. For example, if you create a file called `pages/posts/[id].js`, then it will be accessible at `posts/1`, `posts/2`, etc.

> To learn more about dynamic routing, check the Dynamic Routing documentation.

### Pre-rendering

By default, Next.js **pre-renders** every page. This means that Next.js generates HTML for each page in advance, instead of having it all done by client-side JavaScript. Pre-rendering can result in better performance and SEO.

Each generated HTML is associated with minimal JavaScript code necessary for that page. When a page is loaded by the browser, its JavaScript code runs and makes the page fully interactive. (This process is called *hydration*.)

#### Two forms of Pre-rendering

Next.js has two forms of pre-rendering: **Static Generation** and **Server-side Rendering**. The difference is in **when** it generates the HTML for a page.

* **Static Generation (Recommended)**: The HTML is generated at **build time** and will be reused on each request.
* **Server-side Rendering**: The HTML is generated on **each request**.

Importantly, Next.js lets you **choose** which pre-rendering form you'd like to use for each page. You can create a "hybrid" Next.js app by using Static Generation for most pages and using Server-side Rendering for others.

We **recommend** using **Static Generation** over Server-side Rendering for performance reasons. Statically generated pages can be cached by CDN to boost performance. However, in some cases, Server-side Rendering might be the only option.

Finally, you can always use **Client-side Rendering** along with Static Generation or Server-side Rendering. That means some parts of a page can be rendered entirely by client side JavaScript. To learn more, take a look at the [Data Fetching](https://nextjs.org/docs/basic-features/data-fetching#fetching-data-on-the-client-side) documentation.

### Static Generation (Recommended)

**Examples**

* [Blog Starter using markdown files](https://github.com/vercel/next.js/tree/canary/examples/blog-starter) ([Demo](https://next-blog-starter.now.sh/))
* [DatoCMS Example](https://github.com/vercel/next.js/tree/canary/examples/cms-datocms) ([Demo](https://next-blog-datocms.now.sh/))
* [TakeShape Example](https://github.com/vercel/next.js/tree/canary/examples/cms-takeshape) ([Demo](https://next-blog-takeshape.now.sh/))
* [Sanity Example](https://github.com/vercel/next.js/tree/canary/examples/cms-sanity) ([Demo](https://next-blog-sanity.now.sh/))
* [Prismic Example](https://github.com/vercel/next.js/tree/canary/examples/cms-prismic) ([Demo](https://next-blog-prismic.now.sh/))
* [Contentful Example](https://github.com/vercel/next.js/tree/canary/examples/cms-contentful) ([Demo](https://next-blog-contentful.now.sh/))
* [Static Tweet Demo](https://static-tweet.now.sh/)

If a page uses **Static Generation**, the page HTML is generated at **build time**. That means in production, the page HTML is generated when you run `next build` . This HTML will then be reused on each request. It can be cached by a CDN.

In Next.js, you can statically generate pages **with or without data**. Let's take a look at each case.

#### [Static Generation without data](https://nextjs.org/docs/basic-features/pages#static-generation-without-data)

By default, Next.js pre-renders pages using Static Generation without fetching data. Here's an example:

```javascript
function About() {
  return <div>About</div>
}

export default About
```

Note that this page does not need to fetch any external data to be pre-rendered. In cases like this, Next.js generates a single HTML file per page during build time.

#### Static Generation with data

Some pages require fetching external data for pre-rendering. There are two scenarios, and one or both might apply. In each case, you can use a special function Next.js provides:

1. Your page **content** depends on external data: Use `getStaticProps`.
2. Your page **paths** depend on external data: Use `getStaticPaths` (usually in addition to `getStaticProps`).

**Scenario 1: Your page content depends on external data**

**Example**: Your blog page might need to fetch the list of blog posts from a CMS (content management system).

```javascript
// TODO: Need to fetch `posts` (by calling some API endpoint)
//       before this page can be pre-rendered.
function Blog({ posts }) {
  return (
    <ul>
      {posts.map((post) => (
        <li>{post.title}</li>
      ))}
    </ul>
  )
}

export default Blog
```

To fetch this data on pre-render, Next.js allows you to `export` an `async` function called `getStaticProps` from the same file. This function gets called at build time and lets you pass fetched data to the page's `props` on pre-render.

```javascript
function Blog({ posts }) {
  // Render posts...
}

// This function gets called at build time
export async function getStaticProps() {
  // Call an external API endpoint to get posts
  const res = await fetch('https://.../posts')
  const posts = await res.json()

  // By returning { props: posts }, the Blog component
  // will receive `posts` as a prop at build time
  return {
    props: {
      posts,
    },
  }
}

export default Blog
```

To learn more about how `getStaticProps` works, check out the [Data Fetching documentation](https://tophivetheme.gitbook.io/vurox/getting-started-with-next-js/fetching-data).

**Scenario 2: Your page paths depend on external data**

Next.js allows you to create pages with **dynamic routes**. For example, you can create a file called `pages/posts/[id].js` to show a single blog post based on `id`. This will allow you to show a blog post with `id: 1` when you access `posts/1`.

> To learn more about dynamic routing, check the Dynamic Routing documentation.

However, which `id` you want to pre-render at build time might depend on external data.

**Example**: suppose that you've only added one blog post (with `id: 1`) to the database. In this case, you'd only want to pre-render `posts/1` at build time.

Later, you might add the second post with `id: 2`. Then you'd want to pre-render `posts/2` as well.

So your page **paths** that are pre-rendered depend on external dat&#x61;**.** To handle this, Next.js lets you `export` an `async` function called `getStaticPaths` from a dynamic page (`pages/posts/[id].js` in this case). This function gets called at build time and lets you specify which paths you want to pre-render.

```javascript
// This function gets called at build time
export async function getStaticPaths() {
  // Call an external API endpoint to get posts
  const res = await fetch('https://.../posts')
  const posts = await res.json()

  // Get the paths we want to pre-render based on posts
  const paths = posts.map((post) => `/posts/${post.id}`)

  // We'll pre-render only these paths at build time.
  // { fallback: false } means other routes should 404.
  return { paths, fallback: false }
}
```

Also in `pages/posts/[id].js`, you need to export `getStaticProps` so that you can fetch the data about the post with this `id` and use it to pre-render the page:

```javascript
function Post({ post }) {
  // Render post...
}

export async function getStaticPaths() {
  // ...
}

// This also gets called at build time
export async function getStaticProps({ params }) {
  // params contains the post `id`.
  // If the route is like /posts/1, then params.id is 1
  const res = await fetch(`https://.../posts/${params.id}`)
  const post = await res.json()

  // Pass post data to the page via props
  return { props: { post } }
}

export default Post
```

To learn more about how `getStaticPaths` works, check out the [Data Fetching documentation](https://tophivetheme.gitbook.io/vurox/getting-started-with-next-js/fetching-data).

#### When should I use Static Generation?

We recommend using **Static Generation** (with and without data) whenever possible because your page can be built once and served by CDN, which makes it much faster than having a server render the page on every request.

You can use Static Generation for many types of pages, including:

* Marketing pages
* Blog posts
* E-commerce product listings
* Help and documentation

You should ask yourself: "Can I pre-render this page **ahead** of a user's request?" If the answer is yes, then you should choose Static Generation.

On the other hand, Static Generation is **not** a good idea if you cannot pre-render a page ahead of a user's request. Maybe your page shows frequently updated data, and the page content changes on every request.

In cases like this, you can do one of the following:

* Use Static Generation with **Client-side Rendering:** You can skip pre-rendering some parts of a page and then use client-side JavaScript to populate them. To learn more about this approach, check out the Data Fetching documentation.
* Use **Server-Side Rendering:** Next.js pre-renders a page on each request. It will be slower because the page cannot be cached by a CDN, but the pre-rendered page will always be up-to-date. We'll talk about this approach below.

### Server-side Rendering

> Also referred to as "SSR" or "Dynamic Rendering".

If a page uses **Server-side Rendering**, the page HTML is generated on **each request**.

To use Server-side Rendering for a page, you need to `export` an `async` function called `getServerSideProps`. This function will be called by the server on every request.

For example, suppose that your page needs to pre-render frequently updated data (fetched from an external API). You can write `getServerSideProps` which fetches this data and passes it to `Page` like below:

```javascript
function Page({ data }) {
  // Render data...
}

// This gets called on every request
export async function getServerSideProps() {
  // Fetch data from external API
  const res = await fetch(`https://.../data`)
  const data = await res.json()

  // Pass data to the page via props
  return { props: { data } }
}

export default Page
```

As you can see, `getServerSideProps` is similar to `getStaticProps`, but the difference is that `getServerSideProps` is run on every request instead of on build time.