docs.sheetjs.com/docz/docs/03-demos/04-static/08-nextjs.md

---
title: NextJS
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---

import current from '/version.js';
import Tabs from '@theme/Tabs';
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NextJS is a server-side framework for building static and dynamic sites. For
pure static sites, [Webpack loaders](/docs/demos/static/webpack) can preprocess
files and NextJS can build static pages from spreadsheets. For dynamic sites,
NextJS lifecycle methods can read files on the server side.

The [NodeJS module](/docs/getting-started/installation/nodejs) can be imported
from pages or loaded in Webpack loaders.

:::warning

[`import`](/docs/getting-started/installation/nodejs#esm-import) does not load
NodeJS native modules. The Installation section includes a note on dynamic
import of `fs` within lifecycle methods.

:::

NextJS best practices have evolved over time, but there are three key parts:

1) [Loading Data](#loading-data): NextJS can read files in lifecycle methods OR
custom Webpack loaders can create asset modules.

2) [Lifecycle Methods](#nextjs-strategies): NextJS includes strategies for
static pages (`getStaticProps`) as well as dynamic pages (`getServerSideProps`).

3) [Data Presentation](#data-presentation): Pages use React and JSX.

:::caution Next 13+ and SWC

Next 13 switched to the SWC minifier. There are known issues with the minifier.
Until those issues are resolved, SWC should be disabled in `next.config.js`:

```js title="next.config.js"
module.exports = {
// highlight-next-line
  swcMinify: false
};
```

:::

:::warning Telemetry

NextJS collects telemetry by default. The `telemetry` subcommand can disable it:

```js
npx next@13.4.4 telemetry disable
```

The setting can be verified by running

```js
npx next@13.4.4 telemetry status
```

:::

:::note

The following deployments were tested:

| NextJS | Date       |
|:-------|:-----------|
| 13.1.1 | 2023-01-14 |
| 13.4.4 | 2023-05-26 |

:::

## Loading Data

At a high level, there are two ways to pull spreadsheet data into NextJS apps:
loading an asset module or performing the file read operations from the NextJS
lifecycle methods.

Asset modules are appropriate for static sites when the file names are known in
advance. Performing file read operations in lifecycle methods is more flexible
but does not support live reloading.

### Asset Module

:::caution

When the demo was last tested, Turbopack did not support true raw loaders. For
development use, the normal `npx next dev` should be used.

:::

The following diagram depicts the workbook waltz:

```mermaid
flowchart LR
  file[(workbook\nfile)]
  subgraph SheetJS operations
    base64(base64\nstring)
    aoo(array of\nobjects)
  end
  html{{HTML\nTABLE}}
  file --> |base64-loader.js\ncustom plugin| base64
  base64 --> |page\nlifecycle method| aoo
  aoo --> |page\nIndex method| html
```

In this flow, it is strongly recommended to make a loader return a Base64 string:

```js title="base64-loader.js"
function loader(content) {
  /* since `loader.raw` is true, `content` is a Buffer */
  return `export default '${content.toString("base64")}'`;
}
/* ensure the function receives a Buffer */
loader.raw = true;
module.exports = loader;
```

The webpack configuration is controlled in `next.config.js`:

```js title="next.config.js"
module.exports = {
  webpack: (config) => {
    // highlight-start
    /* add to the webpack config module.rules array */
    config.module.rules.push({
      /* `test` matches file extensions */
      test: /\.(numbers|xls|xlsx|xlsb)/,
      /* use the loader script */
      use: [ { loader: './base64-loader' } ]
    });
    // highlight-end
    return config;
  }
};
```

Module alias directories can be defined in `jsconfig.json` or `tsconfig.json`:

```json title="jsconfig.json"
{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      // highlight-next-line
      "@/*": ["*"]
    }
  }
}
```

Pages can import the files directly. It is strongly recommended to store files
in a `data` folder. This example uses `getStaticProps` to parse `sheetjs.xlsx`:

```jsx title="index.js"
import { read, utils } from 'xlsx';
// highlight-next-line
import base64 from '@/data/sheetjs.xlsx';

export async function getStaticProps() {
  /* parse base64 data */
  // highlight-next-line
  const wb = read(base64, { type: "base64" });
  return { props: {
      /* generate array of objects from the first sheet */
      data: utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]])
  } };
}
```

### Raw Operations

Files can be read using `readFile` in lifecycle methods. The `cwd` method from
the `process` module will point to the root of the project.

The following diagram depicts the workbook waltz:

```mermaid
flowchart LR
  file[(workbook\nfile)]
  subgraph SheetJS operations
    buffer(NodeJS\nBuffer)
    aoo(array of\nobjects)
  end
  html{{HTML\nTABLE}}
  file --> |page\nlifecycle method| buffer
  buffer --> |page\nlifecycle method| aoo
  aoo --> |page\nIndex method| html
```

This example reads the file `sheetjs.xlsx` in the `data` folder in the project:

```js
import { readFile, utils, set_fs } from 'xlsx';
import { join } from 'path';
import { cwd } from 'process';

export async function getServerSideProps() {
// highlight-start
  set_fs(await import("fs")); // dynamically import 'fs' when needed
  const filename = join(cwd(), "data", "sheetjs.xlsx"); // /data/sheetjs.xlsx
  const wb = readFile(filename);
  // highlight-end

  /* generate and return the html from the first worksheet */
  const data = utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]]);
  return { props: { data } };
}
```

:::warning Reading and writing files during the build process

As the NextJS workaround is non-traditional, it bears repeating:

`fs` cannot be statically imported from the top level in NextJS pages.  The
dynamic import must happen within a lifecycle function.

:::


## NextJS Strategies

NextJS currently provides 3 strategies:

- "Static Site Generation" using `getStaticProps`
- "SSG with Dynamic Routes" using `getStaticPaths`
- "Server-Side Rendering" using `getServerSideProps`

### Static Site Generation

When using `getStaticProps`, the file will be read once during build time.
This example reads `sheetjs.xlsx` from the `data` folder:

<Tabs groupId="data">
  <TabItem value="asset" label="Asset Module">

```js
import { read, utils } from 'xlsx';
import base64 from '@/data/sheetjs.xlsx';

export async function getStaticProps() {
  const wb = read(base64, { type: "base64" });

  /* generate and return the html from the first worksheet */
  const html = utils.sheet_to_html(wb.Sheets[wb.SheetNames[0]]);
  return { props: { html } };
};
```

  </TabItem>
  <TabItem value="raw" label="Raw Operations">

```js
import { readFile, set_fs, utils } from 'xlsx';
import { join } from 'path';
import { cwd } from 'process';

export async function getStaticProps() {
  set_fs(await import("fs"));
  const filename = join(cwd(), "data", "sheetjs.xlsx"); // /data/sheetjs.xlsx
  const wb = readFile(filename);

  /* generate and return the html from the first worksheet */
  const html = utils.sheet_to_html(wb.Sheets[wb.SheetNames[0]]);
  return { props: { html } };
};
```

  </TabItem>
</Tabs>

### Dynamic Routes

Typically a static site with dynamic routes has an endpoint `/sheets/[id]` that
implements both `getStaticPaths` and `getStaticProps`.

- `getStaticPaths` should return an array of worksheet indices:

<Tabs groupId="data">
  <TabItem value="asset" label="Asset Module">

```js
import { read } from 'xlsx';
import base64 from '@/data/sheetjs.xlsx';

export async function getStaticPaths() {
  /* read file */
  const wb = read(base64, { type: "base64" });

  /* generate an array of objects that will be used for generating pages */
  const paths = wb.SheetNames.map((name, idx) => ({ params: { id: idx.toString() } }));
  return { paths, fallback: false };
};
```

  </TabItem>
  <TabItem value="raw" label="Raw Operations">

```js
import { readFile, set_fs } from 'xlsx';
import { join } from 'path';
import { cwd } from 'process';

export async function getStaticPaths() {
  /* read file */
  set_fs(await import("fs"));
  const filename = join(cwd(), "data", "sheetjs.xlsx"); // /data/sheetjs.xlsx
  const wb = readFile(path);

  /* generate an array of objects that will be used for generating pages */
  const paths = wb.SheetNames.map((name, idx) => ({ params: { id: idx.toString() } }));
  return { paths, fallback: false };
};
```

  </TabItem>
</Tabs>

:::note

For a pure static site, `fallback` must be set to `false`!

:::

- `getStaticProps` will generate the actual HTML for each page:

<Tabs groupId="data">
  <TabItem value="asset" label="Asset Module">

```js
import { read, utils } from 'xlsx';
import base64 from '@/data/sheetjs.xlsx';

export async function getStaticProps(ctx) {
  /* read file */
  const wb = read(base64, { type: "base64" });

  /* get the corresponding worksheet and generate HTML */
  const ws = wb.Sheets[wb.SheetNames[ctx.params.id]]; // id from getStaticPaths
  const html = utils.sheet_to_html(ws);
  return { props: { html } };
};
```

  </TabItem>
  <TabItem value="raw" label="Raw Operations">

```js
import { readFile, set_fs, utils } from 'xlsx';
import { join } from 'path';
import { cwd } from 'process';

export async function getStaticProps(ctx) {
  /* read file */
  set_fs(await import("fs"));
  const filename = join(cwd(), "data", "sheetjs.xlsx"); // /data/sheetjs.xlsx
  const wb = readFile(path);

  /* get the corresponding worksheet and generate HTML */
  const ws = wb.Sheets[wb.SheetNames[ctx.params.id]]; // id from getStaticPaths
  const html = utils.sheet_to_html(ws);
  return { props: { html } };
};
```

  </TabItem>
</Tabs>

### Server-Side Rendering

:::caution Do not use on a static site

These routes require a NodeJS dynamic server. Static page generation will fail!

`getStaticProps` and `getStaticPaths` support static site generation (SSG).

`getServerSideProps` is suited for NodeJS hosted deployments where the workbook
changes frequently and a static site is undesirable.

:::

When using `getServerSideProps`, the file will be read on each request.

<Tabs groupId="data">
  <TabItem value="asset" label="Asset Module">

:::caution Consider using a static strategy

When using asset modules, the file names and file paths are processed during the
build step. The content is fixed. In this situation, a static approach such as
`getStaticProps` is strongly recommended.

:::

```js
import { read } from 'xlsx';
import base64 from '@/data/sheetjs.xlsx';

export async function getServerSideProps() {
  /* read file */
  const wb = read(base64, { type: "base64" });

  /* generate and return the html from the first worksheet */
  const html = utils.sheet_to_html(wb.Sheets[wb.SheetNames[0]]);
  return { props: { html } };
};
```


  </TabItem>
  <TabItem value="raw" label="Raw Operations">

```js
import { readFile, set_fs, utils } from 'xlsx';
import { join } from 'path';
import { cwd } from 'process';

export async function getServerSideProps() {
  /* read file */
  set_fs(await import("fs"));
  const filename = join(cwd(), "data", "sheetjs.xlsx"); // /data/sheetjs.xlsx
  const wb = readFile(path);

  /* generate and return the html from the first worksheet */
  const html = utils.sheet_to_html(wb.Sheets[wb.SheetNames[0]]);
  return { props: { html } };
};
```

  </TabItem>
</Tabs>

## Data Presentation

[The React demo](/docs/demos/frontend/react) compares common approaches.

### HTML

HTML output can be generated using `XLSX.utils.sheet_to_html` and inserted into
the document using the `dangerouslySetInnerHTML` attribute:

```mermaid
flowchart LR
  subgraph SheetJS operations
    data(File\nData)
    code{{HTML\nTABLE}}
  end
  html{{Rendered\nPage}}
  data --> |lifecycle\nsheet_to_html| code
  code --> |Index\ninnerHTML| html
```

```jsx
export default function Index({html, type}) { return (
  <div dangerouslySetInnerHTML={{ __html: html }} />
); }
```

### Arrays of Objects

Arrays of objects can be generated using `XLSX.utils.sheet_to_json` and inserted
into the document using standard JSX:

```mermaid
flowchart LR
  subgraph SheetJS operations
    data(File\nData)
    aoo(array of\nobjects)
  end
  html{{Rendered\nPage}}
  data --> |lifecycle\nsheet_to_json| aoo
  aoo --> |Index\nReact + JSX| html
```

```jsx
export default function Index({aoo, type}) { return (
  <table><thead><tr key={0}><th>Name</th><th>Index</th></tr></thead><tbody>
// highlight-start
    {aoo.map(row => ( <tr>
      <td>{row.Name}</td>
      <td>{row.Index}</td>
    </tr>))}
// highlight-end
  </tbody></table>
); }
```

## Demo

:::note

This demo showcases the following SheetJS + NextJS flows:

| Page                  | Loading Data | Lifecycle Method     | SheetJS API     |
|:----------------------|:-------------|:---------------------|:----------------|
| `/getStaticProps`     | asset module | `getStaticProps`     | `sheet_to_json` |
| `/sheets/[id]`        | asset module | `getStaticPaths`     | `sheet_to_html` |
| `/getServerSideProps` | lifecycle    | `getServerSideProps` | `sheet_to_html` |

:::

### Initial Setup

0) Disable NextJS telemetry:

```js
npx next@13.4.4 telemetry disable
```

Confirm it is disabled by running

```js
npx next@13.4.4 telemetry status
```

1) Set up folder structure.  At the end, a `pages` folder with a `sheets`
   subfolder must be created.  On Linux or MacOS or WSL:

```bash
mkdir sheetjs-next
cd sheetjs-next
mkdir -p pages/sheets/
```

2) Download the [test file](pathname:///next/sheetjs.xlsx) and place in the
   project root.  On Linux or MacOS or WSL:

```bash
curl -LO https://docs.sheetjs.com/next/sheetjs.xlsx
```

3) Install dependencies:

<CodeBlock language="bash">{`\
npm i --save https://cdn.sheetjs.com/xlsx-${current}/xlsx-${current}.tgz next@13.4.4`}
</CodeBlock>

4) Download NextJS config scripts and place in the root folder:

- [`base64-loader.js`](pathname:///next/base64-loader.js)
- [`jsconfig.json`](pathname:///next/jsconfig.json)
- [`next.config.js`](pathname:///next/next.config.js)
- [`styles.css`](pathname:///next/styles.css)

On Linux or MacOS or WSL:

```bash
curl -LO https://docs.sheetjs.com/next/base64-loader.js
curl -LO https://docs.sheetjs.com/next/jsconfig.json
curl -LO https://docs.sheetjs.com/next/next.config.js
curl -LO https://docs.sheetjs.com/next/styles.css
```

5) Download test scripts:

Download and place the following scripts in the `pages` subfolder:

- [`_app.js`](pathname:///next/_app.js)
- [`index.js`](pathname:///next/index.js)
- [`getServerSideProps.js`](pathname:///next/getServerSideProps.js)
- [`getStaticPaths.js`](pathname:///next/getStaticPaths.js)
- [`getStaticProps.js`](pathname:///next/getStaticProps.js)

Download [`[id].js`](pathname:///next/%5Bid%5D.js) and place in the
`pages/sheets` subfolder.

:::caution Percent-Encoding in the script name

The `[id].js` script must have the literal square brackets in the name. If your
browser saved the file to `%5Bid%5D.js`. rename the file.

:::

On Linux or MacOS or WSL:

```bash
cd pages
curl -LO https://docs.sheetjs.com/next/_app.js
curl -LO https://docs.sheetjs.com/next/index.js
curl -LO https://docs.sheetjs.com/next/getServerSideProps.js
curl -LO https://docs.sheetjs.com/next/getStaticPaths.js
curl -LO https://docs.sheetjs.com/next/getStaticProps.js
cd sheets
curl -LOg 'https://docs.sheetjs.com/next/[id].js'
cd ../..
```

### Testing

6) Test the deployment:

```bash
npx next@13.4.4
```

Open a web browser and access:

- `http://localhost:3000` landing page
- `http://localhost:3000/getStaticProps` shows data from the first sheet
- `http://localhost:3000/getServerSideProps` shows data from the first sheet
- `http://localhost:3000/getStaticPaths` shows a list (2 sheets)

The individual worksheets are available at

- `http://localhost:3000/sheets/0`
- `http://localhost:3000/sheets/1`

7) While the development server is running, open the `/getStaticProps` page and
open `sheetjs.xlsx` with a spreadsheet editor. In the editor, add a row to the
bottom of the "Indices" worksheet.

After saving the file, the website should refresh with the new row.

### Production Build

8) Stop the server and run a production build:

```bash
npx next@13.4.4 build
```

The final output will show a list of the routes and types:

```
Route (pages)                              Size     First Load JS
┌ ○ /                                      563 B          74.4 kB
├   /_app                                  0 B            73.9 kB
├ ○ /404                                   182 B          74.1 kB
├ λ /getServerSideProps                    522 B          74.4 kB
├ ● /getStaticPaths                        2.89 kB        76.8 kB
├ ● /getStaticProps                        586 B          74.5 kB
└ ● /sheets/[id]                           522 B          74.4 kB
    ├ /sheets/0
    └ /sheets/1
```

As explained in the summary, the `/getStaticPaths` and `/getStaticProps` routes
are completely static.  2 `/sheets/#` pages were generated, corresponding to 2
worksheets in the file.  `/getServerSideProps` is server-rendered.

9) Try to build a static site:

```bash
npx next@13.4.4 export
```

:::note The static export will fail!

A static page cannot be generated at this point because `/getServerSideProps`
is still server-rendered.

:::

### Static Site

10) Delete `pages/getServerSideProps.js` and rebuild:

```bash
rm -f pages/getServerSideProps.js
npx next@13.4.4 build
```

Inspecting the output, there should be no lines with the `λ` symbol:

```
Route (pages)                              Size     First Load JS
┌ ○ /                                      563 B          74.4 kB
├   /_app                                  0 B            73.9 kB
├ ○ /404                                   182 B          74.1 kB
├ ● /getStaticPaths                        2.89 kB        76.8 kB
├ ● /getStaticProps                        586 B          74.5 kB
└ ● /sheets/[id]                           522 B          74.4 kB
    ├ /sheets/0
    └ /sheets/1
```

11) Generate the static site:

```bash
npx next@13.4.4 export
```

The static site will be written to the `out` subfolder

12) Serve the static site:

```bash
npx http-server out
```

The command will start a local HTTP server for testing the generated site. Note
that `/getServerSideProps` will 404 since the page was removed.