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** is the pre-rendering method that generates the HTML at **build time**. The pre-rendered HTML is then _reused_ on each request.
- **Server-side Rendering** is the pre-rendering method that generates the HTML on **each request**.

Importantly, Next.js lets you **choose** which pre-rendering form 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.

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This example shows how to use [environment variables in Next.js](https://nextjs.org/docs/basic-features/environment-variables).

The index page ([pages/index.js](pages/index.js)) will show you how to [access environment variables in the server](https://nextjs.org/docs/basic-features/environment-variables#loading-environment-variables), and how to [expose environment variables to the browser](https://nextjs.org/docs/basic-features/environment-variables#exposing-environment-variables-to-the-browser).

## Preview

Preview the example live on [StackBlitz](http://stackblitz.com/):

[![Open in StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/github/vercel/next.js/tree/canary/examples/environment-variables)

## Deploy your own

Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/environment-variables&project-name=environment-variables&repository-name=environment-variables)

## How to use

Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:

```bash
npx create-next-app --example environment-variables environment-variables-app
# or
yarn create next-app --example environment-variables environment-variables-app
```

Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

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This example shows how to use [headers in Next.js](https://nextjs.org/docs/api-reference/next.config.js/headers) to add custom HTTP headers into your Next.js app.

The index page ([`pages/index.js`](pages/index.js)) has a list of links to pages with custom headers set up in [`next.config.js`](next.config.js). Run or deploy the app to see how it works!

## Preview

Preview the example live on [StackBlitz](http://stackblitz.com/):

[![Open in StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/github/vercel/next.js/tree/canary/examples/headers)

## Deploy your own

Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/headers&project-name=headers&repository-name=headers)

## How to use

Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:

```bash
npx create-next-app --example headers headers-app
# or
yarn create next-app --example headers headers-app
```

Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

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Headers Example (5)

Next.js ships with [Fast Refresh](https://nextjs.org/docs/basic-features/fast-refresh) which gives you instantaneous feedback on edits made to your React components.

This demos shows how the state of an auto incrementing value and a classic counter is preserved after edits or if there are errors.

## Preview

Preview the example live on [StackBlitz](http://stackblitz.com/):

[![Open in StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/github/vercel/next.js/tree/canary/examples/fast-refresh-demo)

## Deploy your own

Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/fast-refresh-demo&project-name=fast-refresh-demo&repository-name=fast-refresh-demo)

## How to use

Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:

```bash
npx create-next-app --example fast-refresh-demo fast-refresh-demo-app
# or
yarn create next-app --example fast-refresh-demo fast-refresh-demo-app
```

Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

IMG 20200720 085043

Fast Refresh Demo (5)

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 that case, you can use **Server-Side Rendering**. It will be slower, but the pre-rendered page will always be up-to-date. Or you can skip pre-rendering and use client-side JavaScript to populate data.

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## Demo

### [https://next-blog-contentful.vercel.app/](https://next-blog-contentful.vercel.app/)

## Deploy your own

Using the Deploy Button below, you'll deploy the Next.js project as well as connect it to your Contentful space using the Vercel Contentful Integration.

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https%3A%2F%2Fgithub.com%2Fvercel%2Fnext.js%2Ftree%2Fcanary%2Fexamples%2Fcms-contentful&project-name=nextjs-contentful-blog&repository-name=nextjs-contentful-blog&demo-title=Next.js+Blog&demo-description=Static+blog+with+multiple+authors+using+Preview+Mode&demo-url=https%3A%2F%2Fnext-blog-contentful.vercel.app%2F&demo-image=https%3A%2F%2Fassets.vercel.com%2Fimage%2Fupload%2Fv1625705016%2Ffront%2Fexamples%2FCleanShot_2021-07-07_at_19.43.15_2x.png&integration-ids=oac_aZtAZpDfT1lX3zrnWy7KT9VA&env=CONTENTFUL_PREVIEW_SECRET&envDescription=Any%20URL%20friendly%20value%20to%20secure%20Preview%20Mode)

### Related examples

- [WordPress](/examples/cms-wordpress)
- [DatoCMS](/examples/cms-datocms)
- [Sanity](/examples/cms-sanity)
- [TakeShape](/examples/cms-takeshape)
- [Prismic](/examples/cms-prismic)
- [Strapi](/examples/cms-strapi)
- [Agility CMS](/examples/cms-agilitycms)
- [Cosmic](/examples/cms-cosmic)
- [ButterCMS](/examples/cms-buttercms)
- [Storyblok](/examples/cms-storyblok)
- [GraphCMS](/examples/cms-graphcms)
- [Kontent](/examples/cms-kontent)
- [Ghost](/examples/cms-ghost)
- [Umbraco Heartcore](/examples/cms-umbraco-heartcore)
- [Blog Starter](/examples/blog-starter)

## How to use

Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:

```bash
npx create-next-app --example cms-contentful cms-contentful-app
# or
yarn create next-app --example cms-contentful cms-contentful-app
```

## Configuration

### Step 1. Create an account and a space on Contentful

First, [create an account on Contentful](https://www.contentful.com/sign-up/).

After creating an account, create a new empty **space** from the [dashboard](https://app.contentful.com/) and assign to it any name of your liking.

### Step 2. Create a content model

The [content model](https://www.contentful.com/developers/docs/concepts/data-model/) defines the data structures of your application/websites. The structures are flexible and you can tailor them to your needs.

For this example you need to create a content model that defines an author and a post content type. **You can create these two by running a script or by doing it manually** to familiarize yourself with the Contentful user interface.

#### Run a script to create the content model

This project includes a setup script which you can use to set up the content model expected by the source code.

In your Contentful dashboard go to **Settings > General Settings** and copy the **Space ID**.

Next, go to **Settings > API > Content management tokens** and create a new token by clicking **Generate personal token**. This token has the same access rights as the logged in user. **Do not share it publicly**, you will only use it to set up your space and can delete it afterwards.

With the space ID and management access token at hand run the following command:

```
npx cross-env CONTENTFUL_SPACE_ID=YOUR_SPACE_ID CONTENTFUL_MANAGEMENT_TOKEN=XXX npm run setup
```

This command will create the needed content structures and set up your Contentful space ready to use. The output should look as follows:

```
> cms-contentful@1.0.0 setup /Users/stefan.judis/Projects/next.js/examples/cms-contentful
> node ./contentful/setup.js $CONTENTFUL_SPACE_ID $CONTENTFUL_MANAGEMENT_TOKEN

┌──────────────────────────────────────────────────┐
│ The following entities are going to be imported: │
├─────────────────────────────────┬────────────────┤
│ Content Types                   │ 2              │
├─────────────────────────────────┼────────────────┤
│ Editor Interfaces               │ 2              │
├─────────────────────────────────┼────────────────┤
│ Locales                         │ 1              │
├─────────────────────────────────┼────────────────┤
│ Webhooks                        │ 0              │
├─────────────────────────────────┼────────────────┤
│ Entries                         │ 0              │
├─────────────────────────────────┼────────────────┤
│ Assets                          │ 0              │
└─────────────────────────────────┴────────────────┘
 ✔ Validating content-file
 ✔ Initialize client (1s)
 ✔ Checking if destination space already has any content and retrieving it (2s)
 ✔ Apply transformations to source data (1s)
 ✔ Push content to destination space
   ✔ Connecting to space (1s)
   ...
   ...
   ...
```

#### Create the content model manually

##### Create an `Author` content type

From your contentful space, go to **Content model** and add a new content type:

- Give it the **Name** `Author`, the **Api Identifier** should be `author`

Once the content model is saved, add these fields (you don't have to modify the settings unless specified):

- `name` - **Text** field (type **short text**). **Field ID** should be set to `name`
- `picture` - **Media** field (type **one file**). **Field ID** should be set to `picture`

Save the content type and continue.

##### Create a `post` type

From your contentful space, go to **Content model** and add another content type:

- Give it the **Name** `Post`, the **Api Identifier** should be `post`

Next, add these fields (you don't have to modify the settings unless specified):

- `title` - **Text** field (type **short text**)
- `content` - **Rich text** field
- `excerpt` - **Text** field (type **Long text, full-text search**)
- `coverImage` - **Media** field (type **one file**)
- `date` - **Date and time** field
- `slug` - **Text** field. You can optionally go to the settings of this field, and under **Appearance**, select **Slug** to display it as a slug of the `title` field.
- `author` - **Reference** field (type **one reference**)

Save the content type and continue.

### Step 3. Validate your content model

After setting up the content model (either manually or by running `npm run setup` or `yarn setup`), it should look as follows.

**Content model overview**

![Content model overview](./docs/content-model-overview.jpg)

### Step 4. Populate Content

Go to the **Content** section in your space, then click on **Add entry** and select the **Author** content type:

- You just need **1 author entry**.
- Use dummy data for the text.
- For the image, you can download one from [Unsplash](https://unsplash.com/).

Next, create another entry with the content type **Post**:

- We recommend creating at least **2 post entries**.
- Use dummy data for the text.
- For images, you can download them from [Unsplash](https://unsplash.com/).
- Pick the **author** you created earlier.

**Important:** For each entry and asset, you need to click on **Publish**. If not, the entry will be in draft state.

![Published content entry](./docs/content-entry-publish.jpg)

### Step 5. Set up environment variables

From your contentful space, go to **Settings > API keys**. There will be an example Content delivery / preview token - you can use these API keys. (You may also create a new key.)

Next, copy the `.env.local.example` file in this directory to `.env.local` (which will be ignored by Git):

```bash
cp .env.local.example .env.local
```

Then set each variable on `.env.local`:

- `CONTENTFUL_SPACE_ID` should be the **Space ID** field of your API Key
- `CONTENTFUL_ACCESS_TOKEN` should be the **[Content Delivery API](https://www.contentful.com/developers/docs/references/content-delivery-api/) - access token** field of your API key
- `CONTENTFUL_PREVIEW_ACCESS_TOKEN` should be the **[Content Preview API](https://www.contentful.com/developers/docs/references/content-preview-api/) - access token** field of your API key
- `CONTENTFUL_PREVIEW_SECRET` should be any value you want. It must be URL friendly as the dashboard will send it as a query parameter to enable preview mode

Your `.env.local` file should look like this:

```bash
CONTENTFUL_SPACE_ID=...
CONTENTFUL_ACCESS_TOKEN=...
CONTENTFUL_PREVIEW_ACCESS_TOKEN=...
CONTENTFUL_PREVIEW_SECRET=...
```

### Step 6. Run Next.js in development mode

```bash
npm install
npm run dev

# or

yarn install
yarn dev
```

Your blog should be up and running on [http://localhost:3000](http://localhost:3000)! If it doesn't work, post on [GitHub discussions](https://github.com/vercel/next.js/discussions).

### Step 7. Try preview mode

In your Contentful space, go to **Settings > Content preview** and add a new content preview for development.

The **Name** field may be anything, like `Development`. Then, under **Content preview URLs**, check **Post** and set its value to:

```
http://localhost:3000/api/preview?secret=<CONTENTFUL_PREVIEW_SECRET>&slug={entry.fields.slug}
```

Replace `<CONTENTFUL_PREVIEW_SECRET>` with its respective value in `.env.local`.

![Content preview setup](./docs/content-preview-setup.jpg)

Once saved, go to one of the posts you've created and:

- **Update the title**. For example, you can add `[Draft]` in front of the title.
- The state of the post will switch to **CHANGED** automatically. **Do not** publish it. By doing this, the post will be in draft state.
- In the sidebar, you will see the **Open preview** button. Click on it!

![Content entry overview](./docs/content-entry-preview.jpg)

You will now be able to see the updated title. To exit preview mode, you can click on **Click here to exit preview mode** at the top of the page.

### Step 8. Deploy on Vercel

You can deploy this app to the cloud with [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

#### Deploy Your Local Project

To deploy your local project to Vercel, push it to GitHub/GitLab/Bitbucket and [import to Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example).

**Important**: When you import your project on Vercel, make sure to click on **Environment Variables** and set them to match your `.env.local` file.

#### Deploy from Our Template

Alternatively, you can deploy using our template by clicking on the Deploy button below.

This will deploy the Next.js project as well as connect it to your Contentful space using the Vercel Contentful Integration. If you are using Preview Mode, make sure to add `CONTENTFUL_PREVIEW_SECRET` as an [Environment Variable](https://vercel.com/docs/environment-variables) as well.

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https%3A%2F%2Fgithub.com%2Fvercel%2Fnext.js%2Ftree%2Fcanary%2Fexamples%2Fcms-contentful&project-name=nextjs-contentful-blog&repository-name=nextjs-contentful-blog&demo-title=Next.js+Blog&demo-description=Static+blog+with+multiple+authors+using+Preview+Mode&demo-url=https%3A%2F%2Fnext-blog-contentful.vercel.app%2F&demo-image=https%3A%2F%2Fassets.vercel.com%2Fimage%2Fupload%2Fv1625705016%2Ffront%2Fexamples%2FCleanShot_2021-07-07_at_19.43.15_2x.png&integration-ids=oac_aZtAZpDfT1lX3zrnWy7KT9VA&env=CONTENTFUL_PREVIEW_SECRET&envDescription=Any%20URL%20friendly%20value%20to%20secure%20Preview%20Mode)

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When to Use Static Generation v.s. Server-side Rendering (6)

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A statically generated blog example using Next.js and Contentful (6)

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Environment Variables Example (6)

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A statically generated blog example using Next.js and Contentful (7)

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Two Forms of Pre-rendering (7)

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When to Use Static Generation v.s. Server-side Rendering (8)