Sheets in ExpressJS

ExpressJS is a lightweight NodeJS framework for building server-side applications.

SheetJS is a JavaScript library for reading and writing data from spreadsheets.

This demo uses ExpressJS and SheetJS to read and write data. We'll explore how to parse uploaded files in a POST request handler and respond to GET requests with downloadable spreadsheets.

The "Complete Example" section includes a complete server.

Tested Deployments

This demo was tested on 2024 March 11 using express-formidable@1.2.0 and ExpressJS 4.18.3

Integration Details

The SheetJS NodeJS module can be imported from scripts that use ExpressJS.

Exporting Data to Workbooks (GET)

The SheetJS write method¹ with the option type: "buffer" generates NodeJS Buffer objects containing the raw file data.

ExpressJS can directly handle Buffer data in Response#end².

The exported filename can be specified using Response#attachment³.

The following demo ExpressJS server will respond to GET requests to /download with a XLSX spreadsheet. In this example, the SheetJS aoa_to_sheet method⁴ generates a sheet object and the book_new and book_append_sheet helpers⁵ build the workbook object.

var XLSX = require('xlsx'), express = require('express');

/* create app */
var app = express();

app.get('/download', function(req, res) {
  /* generate workbook object */
  var ws = XLSX.utils.aoa_to_sheet(["SheetJS".split(""), [5,4,3,3,7,9,5]]);
  var wb = XLSX.utils.book_new(); XLSX.utils.book_append_sheet(wb, ws, "Data");
  /* generate buffer */
  var buf = XLSX.write(wb, {type: "buffer", bookType: "xlsx"});
  /* set headers */
  res.attachment("SheetJSExpress.xlsx");
  /* respond with file data */
  res.status(200).end(buf);
});
app.listen(+process.env.PORT||3000);

Parsing Uploaded Files (POST)

The express-formidable middleware is powered by the formidable parser. It adds a files object to the request.

Each value in the files object has a path property which represents the path to the file in the filesystem. The SheetJS readFile method⁶ can read the file and generate a workbook object⁷.

The following demo ExpressJS server will respond to POST requests to /upload. Assuming the upload field of the form data is the file, the SheetJS read method will parse the file. CSV rows are generated from the first worksheet using the SheetJS sheet_to_csv method⁸.

var XLSX = require('xlsx'), express = require('express');

/* create app */
var app = express();
/* add express-formidable middleware */
app.use(require('express-formidable')());
/* route for handling uploaded data */
app.post('/upload', function(req, res) {
  var f = req.files["upload"]; // <input type="file" id="upload" name="upload">
  var wb = XLSX.readFile(f.path);
  /* respond with CSV data from the first sheet */
  res.status(200).end(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]));
});
app.listen(+process.env.PORT||3000);

Complete Example

1. Save the code sample to SheetJSExpressCSV.js:

SheetJSExpressCSV.js

var XLSX = require('xlsx'), express = require('express');

/* create app */
var app = express();
/* add express-formidable middleware */
app.use(require('express-formidable')());
/* route for handling uploaded data */
app.post('/upload', function(req, res) {
  var f = req.files["upload"]; // <input type="file" id="upload" name="upload">
  var wb = XLSX.readFile(f.path);
  /* respond with CSV data from the first sheet */
  res.status(200).end(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]));
});
app.get('/download', function(req, res) {
  /* generate workbook object */
  var ws = XLSX.utils.aoa_to_sheet(["SheetJS".split(""), [5,4,3,3,7,9,5]]);
  var wb = XLSX.utils.book_new(); XLSX.utils.book_append_sheet(wb, ws, "Data");
  /* generate buffer */
  var buf = XLSX.write(wb, {type: "buffer", bookType: "xlsx"});
  /* set headers */
  res.attachment("SheetJSExpress.xlsx");
  /* respond with file data */
  res.status(200).end(buf);
});
app.listen(+process.env.PORT||3000);

2. Install dependencies:

npm i --save https://cdn.sheetjs.com/xlsx-0.20.3/xlsx-0.20.3.tgz express@4.18.3 express-formidable@1.2.0

3. Start server (note: it will not print anything to console when running)

node SheetJSExpressCSV.js

4. Test POST requests using https://docs.sheetjs.com/pres.numbers . The commands should be run in a new terminal window:

curl -LO https://docs.sheetjs.com/pres.numbers
curl -X POST -F upload=@pres.numbers http://localhost:3000/upload

The response should show the data in CSV rows.

5. Test GET requests by opening http://localhost:3000/download in your browser.

It should prompt to download SheetJSExpress.xlsx

Footnotes

1. See write in "Writing Files" ↩

2. See res.end in the ExpressJS documentation. ↩

3. See res.attachment in the ExpressJS documentation. ↩

4. See aoa_to_sheet in "Utilities" ↩

5. See "Workbook Helpers" in "Utilities" for details on book_new and book_append_sheet. ↩

6. See readFile in "Reading Files" ↩

7. See "Workbook Object" ↩

8. See sheet_to_csv in "CSV and Text" ↩