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This demo covers SvelteKit. The Svelte demo covers general client-side strategies.

This demo uses "Base64 Loader" from the ViteJS demo.

SvelteKit projects use ViteJS under the hood. They expose the vite.config.js script. The ViteJS demo examples work as expected!

The following diagram depicts the workbook waltz:


+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.



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.

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}'`;


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:

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

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:

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 = => [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:

/** @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"];

{#each pres as p}<tr>

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


This demo was tested on 2023 April 30 using SvelteKit 1.15.9

Initial Setup

1) Create a new site:

npm create [email protected] 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 and move to a data subdirectory in the root of the project:

mkdir -p data
curl -Lo data/pres.xlsx

3) Install the SheetJS library:

npm i --save

4) Replace the contents of vite.config.js with the contents of the code block named vite.config.js in the "Loader" section

5) Append the lines from src/app.d.ts snippet in the "Types" section 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"

7) Replace the contents of src/routes/+page.svelte with the contents of the code block named src/routes/+page.svelte in "Data Rendering"

Live Reload

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

9) Start the development server:

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:

npm i --save @sveltejs/adapter-static

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

-import adapter from '@sveltejs/adapter-auto';
+import adapter from '@sveltejs/adapter-static';

13) Build the static site:

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.