xhr

XMLHttpRequest and fetch

XMLHttpRequest and fetch browser APIs enable binary data transfer between web browser clients and web servers. Since this library works in web browsers, server conversion work can be offloaded to the client! This demo shows a few common scenarios involving browser APIs and popular wrapper libraries.

Demos

The included demos focus on an editable table. There are two separate flows:

• When the page is accessed, the browser will attempt to download sheetjs.xlsx and read the workbook. The old table will be replaced with an editable table whose contents match the first worksheet. The table is generated using the sheet_to_html utility with editable:true option

• When the upload button is clicked, the browser will generate a new worksheet using table_to_book and build up a new workbook. It will then attempt to generate a file and upload it to the server.

Demo Server

The server.js nodejs server serves static files on GET request. On a POST request to /upload, the server processes the body and looks for uploaded file. It will write the data for the first file to the indicated file name.

To start the demo, run npm start and navigate to http://localhost:7262/

XMLHttpRequest

For downloading data, the arraybuffer response type generates an ArrayBuffer that can be viewed as an Uint8Array and fed to XLSX.read using array type:

/* set up an async GET request */
var req = new XMLHttpRequest();
req.open("GET", url, true);
req.responseType = "arraybuffer";

req.onload = function(e) {
  /* parse the data when it is received */
  var data = new Uint8Array(req.response);
  var workbook = XLSX.read(data, {type:"array"});
  /* DO SOMETHING WITH workbook HERE */
};
req.send();

For uploading data, this demo populates a FormData object with an ArrayBuffer generated with the array output type:

/* generate XLSX as array buffer */
var data = XLSX.write(workbook, {bookType: 'xlsx', type: 'array'});

/* build FormData with the generated file */
var fd = new FormData();
fd.append('data', new File([data], 'sheetjs.xlsx'));

/* send data */
var req = new XMLHttpRequest();
req.open("POST", "/upload", true);
req.send(fd);

superagent Wrapper Library

The superagent library usage mirrors XHR:

/* set up an async GET request with superagent */
superagent.get(url).responseType('arraybuffer').end(function(err, res) {
  /* parse the data when it is received */
  var data = new Uint8Array(res.body);
  var workbook = XLSX.read(data, {type:"array"});

  /* DO SOMETHING WITH workbook HERE */
});

The upload portion only differs in the actual request command:

/* send data (fd is the FormData object) */
superagent.post("/upload").send(fd);

axios Wrapper Library

The axios library presents a Promise interface. The axios demo uses a single promise, but for production deployments it may make sense to separate parsing:

/* set up an async GET request with axios */
axios(url, {responseType:'arraybuffer'}).catch(function(err) {
  /* error in getting data */
}).then(function(res) {
  /* parse the data when it is received */
  var data = new Uint8Array(res.data);
  var workbook = XLSX.read(data, {type:"array"});
  return workbook;
}).catch(function(err) {
  /* error in parsing */
}).then(function(workbook) {
  /* DO SOMETHING WITH workbook HERE */
});

The upload portion only differs in the actual request command:

/* send data (fd is the FormData object) */
axios("/upload", {method: "POST", data: fd});

fetch

For downloading data, response.arrayBuffer() resolves to an ArrayBuffer that can be converted to Uint8Array and passed to XLSX.read:

fetch(url).then(function(res) {
  /* get the data as a Blob */
  if(!res.ok) throw new Error("fetch failed");
  return res.arrayBuffer();
}).then(function(ab) {
  /* parse the data when it is received */
  var data = new Uint8Array(ab);
  var workbook = XLSX.read(data, {type:"array"});

  /* DO SOMETHING WITH workbook HERE */
});

The upload code is identical to axios, except for the variable name:

fetch("/upload", {method: "POST", body: fd});