| --- |
| 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. |
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|
