next.js/examples/blog/pages/posts/pages.md

---
title: Next.js Pages
date: 2021/3/18
description: Learn more about Next.js pages.
tag: web development
author: You
---

# Next.js Pages

In Next.js, a **page** is a [React Component](https://react.dev/reference/react/Component) 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`.

```
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](/docs/routing/dynamic-routes.md).

## 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)**](#static-generation-recommended): The HTML is generated at **build time** and will be reused on each request.
- [**Server-side Rendering**](#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 with no extra configuration to boost performance. However, in some cases, Server-side Rendering might be the only option.

You can also 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](/docs/basic-features/data-fetching/client-side.md) documentation.

## Static Generation (Recommended)

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

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

```
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).

```
// 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.

```
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](/docs/basic-features/data-fetching/get-static-props.md).

#### 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](/docs/routing/dynamic-routes.md).

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 data**.** 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.

```
// 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) => ({
    params: { id: 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:

```
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](/docs/basic-features/data-fetching/get-static-paths.md).

### 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](/docs/basic-features/data-fetching/client-side.md).
- 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:

```
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.

To learn more about how `getServerSideProps` works, check out our [Data Fetching documentation](/docs/basic-features/data-fetching/get-server-side-props.md)

## Summary

We've discussed two forms of pre-rendering for Next.js.

- **Static Generation (Recommended):** The HTML is generated at **build time** and will be reused on each request. To make a page use Static Generation, either export the page component, or export `getStaticProps` (and `getStaticPaths` if necessary). It's great for pages that can be pre-rendered ahead of a user's request. You can also use it with Client-side Rendering to bring in additional data.
- **Server-side Rendering:** The HTML is generated on **each request**. To make a page use Server-side Rendering, export `getServerSideProps`. Because Server-side Rendering results in slower performance than Static Generation, use this only if absolutely necessary.