docs.sheetjs.com/docz/docs/03-demos/04-static/11-svelte.md

---
title: SvelteKit
pagination_prev: demos/net/index
pagination_next: demos/mobile/index
---

import current from '/version.js';

:::note

This demo covers SvelteKit. The [Svelte demo](/docs/demos/frontend/svelte)
covers general client-side strategies.

This demo uses ["Base64 Loader"](/docs/demos/static/vitejs#base64-loader)
from the ViteJS demo.

:::

SvelteKit projects use ViteJS under the hood. They expose the `vite.config.js`
script. The [ViteJS demo](/docs/demos/static/vitejs) examples work as expected!

The following diagram depicts the workbook waltz:

```mermaid
flowchart LR
  file[(workbook\nfile)]
  subgraph SheetJS operations
    base64(base64\nstring)
    aoa(array of\nobjects)
  end
  html{{HTML\nTABLE}}
  file --> |vite.config.js\ndata loader| base64
  base64 --> |+page.server.js\nload function| aoa
  aoa --> |+page.svelte\ncomponent| html
```

## Integration

`+page.server.js` scripts can be pre-rendered by exporting `prerender` from the
script. If the SheetJS operations are performed in the server script, only the
results will be added to the generated pages!

For static site generation, `@sveltejs/adapter-static` must be used.

### Loader

:::note

The ViteJS demo used the query `?b64` to identify files. To play nice with
SvelteKit, this demo matches the file extensions directly.

:::

The loader should be added to `vite.config.js`. The code is nearly identical to
the ["Base64 Loader" ViteJS example.](/docs/demos/static/vitejs#base64-loader)

```js title="vite.config.js"
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';
import { readFileSync } from 'fs';

export default defineConfig({
  assetsInclude: ['**/*.numbers', '**/*.xlsx'],
  plugins: [sveltekit(), {
    name: "sheet-base64",
    transform(code, id) {
      if(!id.match(/\.(numbers|xlsx)$/)) return;
      var data = readFileSync(id, "base64");
      return `export default '${data}'`;
    }
  }]
});
```

#### Types

For VSCodium integration, types can be specified in `src/app.d.ts`.

The example data loader returns Base64 strings. Declarations should be added for
each file extension supported in the loader:

```ts title="src/app.d.ts"
declare global {
  declare module '*.numbers' {
    const data: string;
    export default data;
  }
  declare module '*.xlsx' {
    const data: string;
    export default data;
  }
}
```

### Data Processing

For static sites, SheetJS operations should be run in `+page.server.js` .

Assuming `pres.xlsx` is stored in the `data` directory from the project root,
the relative import

```js
import b64 from "../../data/pres.xlsx"
```

will return a Base64 string which can be parsed in the script. The workbook
object can be post-processed using utility functions.  The following example
uses `sheet_to_json` to generate arrays of row objects for each worksheet. The
data presented to the page will be an object whose keys are worksheet names:

```js title="src/routes/+page.server.js"
import b64 from "../../data/pres.xlsx";
import { read, utils } from "xlsx";

export const prerender = true;

/** @type {import('./$types').PageServerLoad} */
export async function load({ params }) {
  const wb = read(b64);
  /** @type {[string, any[]][]} */
  const data = wb.SheetNames.map(n => [n, utils.sheet_to_json(wb.Sheets[n])]);
  return Object.fromEntries(data);
}
```

### Data Rendering

The shape of the data is determined by the loader. The example loader returns an
object whose keys are worksheet names and whose values are arrays of objects.

Using standard Svelte patterns, HTML tables can be generated from the data:

```html title="src/routes/+page.svelte"
<script>
  /** @type {import('./$types').PageData} */
  export let data;

  /* `pres` will be the data from Sheet1 */
  /** @type {Array<{Name: string, Index: number}>}*/
  export let pres = data["Sheet1"];
</script>

<h1>Presidents</h1>
<table><thead><th>Name</th><th>Index</th></thead><tbody>
  {#each pres as p}<tr>
    <td>{p.Name}</td>
    <td>{p.Index}</td>
  </tr>{/each}
</tbody></table>
```

When built using `npm run build`, SvelteKit will perform the conversion and emit
a simple HTML table without any reference to the existing spreadsheet file!

## Complete Example

:::note

This demo was tested on 2023 April 30 using SvelteKit `1.15.9`

:::

### Initial Setup

1) Create a new site:

```bash
npm create svelte@latest sheetjs-svelte
cd sheetjs-svelte
npm i
```

When prompted:

- `Which Svelte app template?` select `Skeleton Project`
- `Add type checking with TypeScript?` select `Yes, using JavaScript with JSDoc`
- `Select additional options` press Enter (do not select options)

2) Fetch the example file [`pres.xlsx`](https://sheetjs.com/pres.xlsx) and move
to a `data` subdirectory in the root of the project:

```bash
mkdir -p data
curl -Lo data/pres.xlsx https://sheetjs.com/pres.xlsx
```

3) Install the SheetJS library:

<pre><code parentName="pre" {...{"className": "language-bash"}}>{`\
npm i --save https://cdn.sheetjs.com/xlsx-${current}/xlsx-${current}.tgz`}
</code></pre>

4) Replace the contents of `vite.config.js` with the contents of the code block
named [`vite.config.js` in the "Loader" section](#loader)

5) Append the lines from [`src/app.d.ts` snippet in the "Types" section](#types)
to the `src/app.d.ts` file.

6) Replace the contents of `src/routes/+page.server.ts` with the contents of the
code block named [`src/routes/+page.server.ts` in "Data Processing"](#data-processing)

7) Replace the contents of `src/routes/+page.svelte` with the contents of the
code block named [`src/routes/+page.svelte` in "Data Rendering"](#data-rendering)

### Live Reload

8) Open `data/pres.xlsx` in a spreadsheet editor like Apple Numbers or Excel.

9) Start the development server:

```bash
npm run dev
```

Open the displayed URL (typically `http://localhost:5173`) in a web browser and
observe that the data from the spreadsheet is displayed in the page.

10) In the spreadsheet, set cell A7 to `SheetJS Dev` and cell B7 to `47`.  Save
the file.  After saving, the browser should automatically refresh with new data.

### Static Site

11) Stop the development server and install the static adapter:

```bash
npm install --save @sveltejs/adapter-static
```

12) Edit `svelte.config.js` to use the new adapter:

```diff title="svelte.config.js"
-import adapter from '@sveltejs/adapter-auto';
+import adapter from '@sveltejs/adapter-static';
```

13) Build the static site:

```bash
npm run build
```

14) Open a web browser and access the displayed URL (`http://localhost:8080`).
View the page source and confirm that the raw HTML table includes the data.