---
sidebar_position: 6
title: HTTP Network Requests
---
# XHR 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.
:::caution Third-Party Hosts and Binary Data
Some services like AWS will corrupt raw binary uploads / downloads by encoding
requests and responses in UTF-8. Typically, these services have options for
disabling this behavior.
For AWS, in the "Binary Media Types" section of the API Gateway console, the
following types should be added to ensure smooth uploads and downloads:
- `"multipart/form-data"` (for Lambda functions to receive files from clients)
- `"application/vnd.ms-excel"` (for Lambda functions to send files to clients)
:::
## Downloading Binary Data
Most interesting spreadsheet files are binary data that contain byte sequences
that represent invalid UTF-8 characters.
The APIs generally have a way to control the interpretation of the downloaded
data. The `arraybuffer` response type usually forces the data to be presented
as a pure `ArrayBuffer` which can be parsed directly with `XLSX.read`.
For example, with `fetch`:
```js
const res = await fetch("https://sheetjs.com/pres.numbers");
const ab = await res.arrayBuffer(); // recover data as ArrayBuffer
const wb = XLSX.read(ab);
```
## Uploading Binary Data
`FormData` objects can hold `File` blobs generated from `XLSX.write`:
```js
/* generate XLSX file bytes */
var data = XLSX.write(workbook, {bookType: 'xlsx', type: 'array'});
/* build FormData with the generated file */
var fdata = new FormData();
fdata.append('data', new File([data], 'sheetjs.xlsx'));
// field name ^^^^ file name ^^^^^^^^^^^^
```
The `FormData` object can be passed along to the POST request. For example:
```js
var req = new XMLHttpRequest();
req.open("POST", "/upload", true);
req.send(fdata);
```
## Browser 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
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, upload it to and show the response.
### 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:
```js
/* 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();
```
Live Download demo (click to show)
This demo uses `XMLHttpRequest` to download
and show the data in an HTML table.
```jsx live
function SheetJSXHRDL() {
const [html, setHTML] = React.useState("");
/* Fetch and update HTML */
React.useEffect(async() => {
/* Fetch file */
const req = new XMLHttpRequest();
req.open("GET", "https://sheetjs.com/pres.numbers", true);
req.responseType = "arraybuffer";
req.onload = e => {
/* Parse file */
const wb = XLSX.read(new Uint8Array(req.response));
const ws = wb.Sheets[wb.SheetNames[0]];
/* Generate HTML */
setHTML(XLSX.utils.sheet_to_html(ws));
};
req.send();
}, []);
return ();
}
```
For uploading data, this demo populates a `FormData` object with an ArrayBuffer
generated with the `array` output type:
```js
/* 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", url, true);
req.send(fd);
```
Live Upload demo (click to show)
This demo uses `XMLHttpRequest` to upload data to . It
will parse the workbook and return an HTML table.
```jsx live
function SheetJSXHRUL() {
const [html, setHTML] = React.useState("");
const [sz, setSz] = React.useState(0);
const csv = "a,b,c\n1,2,3";
/* Fetch and update HTML */
const xport = React.useCallback(async() => {
/* Make Workbook from CSV */
const wb = XLSX.read(csv, { type: "string" });
/* Make FormData */
const data = XLSX.write(wb, {bookType: 'xlsx', type: 'array'});
setSz(data.length || data.byteLength);
const fdata = new FormData();
fdata.append('file', new File([data], 'sheetjs.xlsx'));
/* Upload */
const url = "https://s2c.sheetjs.com";
const req = new XMLHttpRequest();
req.open("POST", url, true);
req.onload = (e) => setHTML(req.responseText);
req.send(fdata);
});
return (
CSV Data
{csv}
{sz ? (<>
Generated file size: {sz} bytes
) : ()}
);
}
```
### fetch
For downloading data, `Response#arrayBuffer` resolves to an `ArrayBuffer` that
can be converted to `Uint8Array` and passed to `XLSX.read`:
```js
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 */
});
```
Live Download demo (click to show)
This demo uses `fetch` to download and show
the data in an HTML table.
```jsx live
function SheetJSFetchDL() {
const [html, setHTML] = React.useState("");
/* Fetch and update HTML */
React.useEffect(async() => {
/* Fetch file */
const res = await fetch("https://sheetjs.com/pres.numbers");
const ab = await res.arrayBuffer();
/* Parse file */
const wb = XLSX.read(ab);
const ws = wb.Sheets[wb.SheetNames[0]];
/* Generate HTML */
setHTML(XLSX.utils.sheet_to_html(ws));
}, []);
return ();
}
```
`fetch` takes a second parameter which allows for setting POST request body:
```js
// assuming `fdata` is a FormData object from "Uploading Binary Data" section
fetch("/upload", { method: "POST", body: fdata });
```
Live Upload demo (click to show)
This demo uses `fetch` to upload data to . It will parse
the workbook and return an HTML table.
```jsx live
function SheetJSFetchUL() {
const [html, setHTML] = React.useState("");
const [sz, setSz] = React.useState(0);
const csv = "a,b,c\n1,2,3";
/* Fetch and update HTML */
const xport = React.useCallback(async(e) => {
/* Make Workbook from CSV */
const wb = XLSX.read(csv, { type: "string" });
const data = XLSX.write(wb, {bookType: 'xlsx', type: 'array'});
/* Make FormData */
setSz(data.length || data.byteLength);
const fdata = new FormData();
fdata.append('file', new File([data], 'sheetjs.xlsx'));
/* Upload */
const url = "https://s2c.sheetjs.com";
const res = await fetch(url, {method:"POST", body: fdata});
/* Set HTML */
setHTML((await res.text()));
});
return (
CSV Data
{csv}
{sz ? (<>
Generated file size: {sz} bytes
) : ()}
);
}
```
### Wrapper Libraries
Before `fetch` shipped with browsers, there were various wrapper libraries to
simplify `XMLHttpRequest`. Due to limitations with `fetch`, these libraries
are still relevant.
#### axios
The `axios` library presents a Promise interface. Setting `responseType` to
`arraybuffer` ensures the return type is an ArrayBuffer:
```js
async function workbook_dl_axios(url) {
const res = await axios(url, {responseType:'arraybuffer'});
const workbook = XLSX.read(res.data);
return workbook;
}
```
Live Download demo (click to show)
This demo uses `axios` to download and show
the data in an HTML table.
```jsx live
function SheetJSAxiosDL() {
const [html, setHTML] = React.useState("");
/* Fetch and update HTML */
React.useEffect(async() => {
/* Fetch file */
const res = await axios("https://sheetjs.com/pres.numbers", {responseType: "arraybuffer"});
/* Parse file */
const wb = XLSX.read(res.data);
const ws = wb.Sheets[wb.SheetNames[0]];
/* Generate HTML */
setHTML(XLSX.utils.sheet_to_html(ws));
}, []);
return ();
}
```
Uploading form data is nearly identical to the `fetch` example:
```js
axios("/upload", { method: "POST", data: fdata });
```
Live Upload demo (click to show)
This demo uses `axios` to upload data to . It will parse
the workbook and return an HTML table.
```jsx live
function SheetJSAxiosUL() {
const [html, setHTML] = React.useState("");
const [sz, setSz] = React.useState(0);
const csv = "a,b,c\n1,2,3";
/* Fetch and update HTML */
const xport = React.useCallback(async() => {
/* Make Workbook from CSV */
const wb = XLSX.read(csv, { type: "string" });
/* Make FormData */
const data = XLSX.write(wb, {bookType: 'xlsx', type: 'array'});
setSz(data.length || data.byteLength);
const fdata = new FormData();
fdata.append('file', new File([data], 'sheetjs.xlsx'));
/* Upload */
const url = "https://s2c.sheetjs.com";
const res = await axios(url, {method:"POST", data: fdata});
/* Set HTML */
setHTML(res.data);
});
return (
CSV Data
{csv}
{sz ? (<>
Generated file size: {sz} bytes
) : ()}
);
}
```
#### superagent
The `superagent` library usage mirrors XHR:
```js
/* 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 */
});
```
Live Download demo (click to show)
This demo uses `superagent` to download and
show the data in an HTML table.
```jsx live
function SheetJSSuperAgentDL() {
const [html, setHTML] = React.useState("");
/* Fetch and update HTML */
React.useEffect(async() => {
/* Fetch file */
superagent
.get("https://sheetjs.com/pres.numbers")
.responseType("arraybuffer")
.end((err, res) => {
/* Parse file */
const wb = XLSX.read(res.body);
const ws = wb.Sheets[wb.SheetNames[0]];
/* Generate HTML */
setHTML(XLSX.utils.sheet_to_html(ws));
});
}, []);
return ();
}
```
The upload portion only differs in the actual request command:
```js
/* send data (fd is the FormData object) */
superagent.post("/upload").send(fd);
```
Live Upload demo (click to show)
This demo uses `superagent` to upload data to . It will
parse the workbook and return an HTML table.
```jsx live
function SheetJSSuperAgentUL() {
const [html, setHTML] = React.useState("");
const [sz, setSz] = React.useState(0);
const csv = "a,b,c\n1,2,3";
/* Fetch and update HTML */
const xport = React.useCallback(async() => {
/* Make Workbook from CSV */
const wb = XLSX.read(csv, { type: "string" });
/* Make FormData */
const data = XLSX.write(wb, {bookType: 'xlsx', type: 'array'});
setSz(data.length || data.byteLength);
const fdata = new FormData();
fdata.append('file', new File([data], 'sheetjs.xlsx'));
/* Upload */
const url = "https://s2c.sheetjs.com";
superagent.post(url).send(fdata).end((err, res) => {
/* Set HTML */
setHTML(res.text);
});
});
return (