docs.sheetjs.com/docz/docs/03-demos/27-local/01-file.md

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---
title: Local File Access
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pagination_prev: demos/data/index
pagination_next: demos/cloud/index
sidebar_custom_props:
summary: Reading and writing files using various platform APIs
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---
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import current from '/version.js';
import CodeBlock from '@theme/CodeBlock';
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Reading from and writing to files requires native platform support.
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SheetJS `readFile` and `writeFile` methods include support for some platforms.
Due to sandboxing and security settings, `readFile` does not work in the web
browser and `writeFile` is not guaranteed to work in all cases.
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This demo looks at various web APIs for reading and writing files. We'll explore
how to pass data between SheetJS functions and various APIs.
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:::note pass
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Some snippets are also available in the "Common Use Cases" section:
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- [Data Import](/docs/solutions/input)
- [Data Export](/docs/solutions/output)
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Other demos cover APIs for local file access on special platforms:
- ["iOS and Android Apps"](/docs/demos/mobile/) covers mobile app frameworks
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- ["Desktop Apps"](/docs/demos/desktop/) covers desktop apps
- ["Command-Line Tools"](/docs/demos/cli) covers standalone command-line tools
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:::
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## Binary Data
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JavaScript engines represent binary data in a number of structures.
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The `type` option for SheetJS `read` function[^1] controls how the data should
be interpreted. This parameter distinguishes [binary strings](#binary-strings)
from [Base64 strings](#base64-strings).
The `type` option for SheetJS `write` function[^2] controls the output storage.
### `Uint8Array` and `Buffer`
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A `Uint8Array` is a Typed Array where each value is a 8-bit unsigned integer.
Server-side platforms including NodeJS typically use `Uint8Array`, or a subclass
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such as `Buffer`[^3], to represent data from files.
The SheetJS `read` method can read data from `Uint8Array` without any options:
```js
const wb = XLSX.read(u8);
```
The SheetJS `write` method can generate workbooks stored in
`Uint8Array` structures with the option `type: "buffer"`:
```js
const u8 = XLSX.write(wb, {bookType: "xlsx", type: "buffer"});
```
:::note pass
In NodeJS, the `write` method will generate a `Buffer` instance.
:::
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### `ArrayBuffer`
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An `ArrayBuffer` represents an array of bytes. The `Uint8Array` constructor can
synchronously create a view without copying the underlying data:
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```js
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/* create a Uint8Array "view" */
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const u8 = new Uint8Array(array_buffer);
```
The SheetJS `read` method can read data from `ArrayBuffer` without special
options, as it performs the aforementioned conversion. The SheetJS `write`
method can generate workbooks stored in `ArrayBuffer` structures with the
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option `type: "array"`
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### `Blob` and `File`
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`Blob` is an opaque pointer to data. The data is not immediately accessible.
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`File` extends `Blob` with support for storing file names and other metadata.
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The SheetJS `read` method does not handle `Blob` or `File`. The underlying data
must be pulled into an `ArrayBuffer` before parsing. There are two approaches:
A) Modern browsers support the `arrayBuffer` method. It returns a promise that
resolves to `ArrayBuffer`:
```js
// usage: const wb = await blob_to_wb(blob);
async function blob_to_wb(blob) {
const ab = await blob.arrayBuffer(); // pull data from Blob
return XLSX.read(ab); // parse ArrayBuffer
}
```
B) For broader browser support, the `FileReader` API can pull `ArrayBuffer` data
using the `readAsArrayBuffer` method:
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```js
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// usage: file_to_wb(file, function(wb) { /* wb is a workbook object */ });
function file_to_wb(file, callback) {
var reader = new FileReader();
reader.onload = function(e) {
/* e.target.result is an ArrayBuffer */
callback(XLSX.read(e.target.result));
};
reader.readAsArrayBuffer(file);
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}
```
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<details><summary><b>FileReaderSync in Web Workers</b> (click to show)</summary>
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`FileReaderSync` is only available in Web Workers. It returns an `ArrayBuffer`:
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```js
// assuming main thread called worker.postMessage({ file: file_object })
self.addEventListener('message', (e) => {
/* get file object from message */
var file = e.data.file;
/* Read file data */
const ab = new FileReaderSync().readAsArrayBuffer(file);
/* Parse file */
const wb = XLSX.read(ab);
/* DO SOMETHING WITH wb HERE */
});
```
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["User-Submitted File" example](/docs/demos/bigdata/worker#user-submitted-file)
includes a live demo.
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</details>
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The SheetJS `write` method can generate a `Uint8Array` which can be passed to
the `Blob` constructor:
```js
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function wb_to_blob(wb, bookType) {
/* write workbook to Uint8Array */
const u8 = XLSX.write(wb, { bookType: bookType || "xlsx", type: "buffer" });
/* create array of parts */
const parts = [ u8 ]; // `Blob` constructor expects this
/* create Blob */
const blob = new Blob(parts, { type: "application/vnd.ms-excel" });
return blob;
}
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```
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The `File` constructor accepts an additional `name` argument:
```js
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function wb_to_file(wb, filename) {
/* impute bookType from file extension */
const ext = filename.slice(filename.lastIndexOf(".") + 1);
/* write workbook to Uint8Array */
const u8 = XLSX.write(wb, { bookType: ext, type: "buffer" });
/* create array of parts */
const parts = [ u8 ]; // `File` constructor expects this
/* create File */
const file = new File(parts, filename, { type: "application/vnd.ms-excel" });
return file;
}
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```
### Binary Strings
Binary strings are strings where each character code is between `0` and `255`.
This structure is generated from the `FileReader#readAsBinaryString` method.
The SheetJS `read` method supports binary strings with `type: "binary"`. The
following snippet shows how `readAsBinaryString` can be paired with SheetJS:
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```js
// usage: file_bs_to_wb(file, function(wb) { /* wb is a workbook object */ });
function file_bs_to_wb(file, callback) {
var reader = new FileReader();
reader.onload = function(e) {
/* e.target.result is a binary string */
callback(XLSX.read(e.target.result, { type: "binary" }));
};
reader.readAsBinaryString(file);
}
```
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The SheetJS `write` method can generate binary strings using `type: "binary"`:
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```js
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/* write workbook to binary string */
const bstr = XLSX.write(wb, { bookType: "xlsx", type: "binary" });
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```
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### Base64 Strings
Base64 strings are encoded using 64 display ASCII characters. This structure is
generated from `btoa`, the `FileReader#readAsDataURL` method, and many platform
APIs in mobile and desktop app frameworks.
The SheetJS `read` method supports Base64 strings with `type: "base64"`. The
following snippet shows how `readAsDataURL` can be paired with SheetJS:
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```js
// usage: file_b64_to_wb(file, function(wb) { /* wb is a workbook object */ });
function file_b64_to_wb(file, callback) {
var reader = new FileReader();
reader.onload = function(e) {
/* e.target.result is a base64 string */
callback(XLSX.read(e.target.result, { type: "base64" }));
};
reader.readAsDataURL(file);
}
```
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The SheetJS `write` method can generate Base64 strings using `type: "base64"`:
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```js
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/* write workbook to Base64 string */
const b64 = XLSX.write(wb, { bookType: "xlsx", type: "base64" });
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```
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### Arrays of Numbers
Some platforms represent binary data as arrays of numbers, where each number
represents one byte in the file.
The SheetJS `read` method supports arrays of unsigned bytes (where each value
is between `0` and `255`) with `type: "array"`.
:::caution Java and Signed Bytes
[Google Sheets](/docs/demos/extensions/gsheet) follows Java signed data type
conventions. Byte arrays include values from `-128` to `127`.
<details><summary><b>How to Fix Signed Arrays</b> (click to show)</summary>
The unsigned value for a negative byte can be calculated with a bitwise AND
(`&`) operation against `0xFF`:
```js
const unsigned_byte = signed_byte & 0xFF;
```
For legacy platforms including [NetSuite](/docs/demos/cloud/netsuite) 2.0, the
bitwise AND assignment operator (`&=`) can rectify an array in place:
```js
/* convert a signed byte array to an unsigned byte array in place */
for(var i = 0; i < array.length; ++i) array[i] &= 0xFF;
```
For modern platforms, the `Uint8Array` constructor understands signed bytes:
```js
/* copy data into a new Uint8Array */
const u8 = new Uint8Array(array);
```
</details>
:::
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## Web Browsers
:::warning pass
Not all web APIs are supported in all browsers. For example, Firefox does not
support the "File System Access API".
Even when a browser technically supports a web API, it may be disabled in the
client browser. Some APIs do not give any feedback.
:::
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### HTML5 Download Attribute
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_Writing Files_
`writeFile` will attempt a download in the browser using the attribute.
```js
XLSX.writeFile(wb, "SheetJS.xlsx");
```
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<details><summary><b>Implementation Details</b> (click to show)</summary>
Under the hood, it creates a special URL and clicks a link. The library method
includes a few workarounds for legacy browsers
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**`XLSX.writeFile(wb, "SheetJS.xlsx");`** is roughly equivalent to:
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```js
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/* write data -- `writeFile` infers bookType from filename but `write` cannot */
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const u8 = XLSX.write(wb, { bookType: "xlsx", type: "buffer" });
/* create Blob */
const blob = new Blob([u8]);
/* create object URL */
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const url = URL.createObjectURL(blob);
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/* create `A` DOM element */
const a = document.createElement("a");
/* set export file name */
a.download = "SheetJS.xlsx";
/* wire up the object URL to the DOM element */
a.href = url;
/* add to the page */
document.body.appendChild(a);
/* click the link */
a.click();
/* remove the element from the page */
document.body.removeChild(a);
```
</details>
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:::caution Web Workers
`XLSX.writeFile` requires DOM access and will not work in a Web Worker!
The workaround is to generate the file data from the Worker (using `XLSX.write`)
and send the data back to the main context for the actual download action.
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["Creating a Local File"](/docs/demos/bigdata/worker#creating-a-local-file)
includes a live demo.
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:::
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#### Google Tag Manager
:::caution pass
Google Tag Manager is known to intercept and corrupt links. This issue will
manifest as UUID file names like `01234567-89ab-cdef-0123-456789abcdef` .
:::
For sites using GTM, it is recommended to patch `document.createElement` and
revert after performing the export.
<details><summary><b>GTM Workaround</b> (click to show)</summary>
The workaround is to ensure new `A` elements created by `document.createElement`
have the `target` attribute set to `_blank`.
After calling `writeFile`, the old version of the method should be restored.
```js title="GTM Workaround"
/* preparation */
document.createElement2 = document.createElement;
document.createElement = function(...args) {
if(args.length == 1 && args[0].toLowerCase() == "a") {
const a = document.createElement2("a");
a.target = "_blank";
return a;
}
return document.createElement2.call(this, ...args);
};
/* export (XLSX.writeFile) */
XLSX.writeFile(wb, "SheetJS.xlsx");
/* cleanup */
setTimeout(() => {
document.createElement = document.createElement2;
delete document.createElement2;
}, 1000);
```
</details>
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### File API
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_Reading Files_
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In the `change` event of `<input type="file">`, the event object will have a
`target` property. The `files` property of `target` is a list of `File` objects.
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```js
async function handleFileAsync(e) {
/* get first file */
const file = e.target.files[0];
/* get raw data */
const data = await file.arrayBuffer();
/* data is an ArrayBuffer */
const workbook = XLSX.read(data);
/* do something with the workbook here */
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console.log(XLSX.utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]]));
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}
input_dom_element.addEventListener("change", handleFileAsync, false);
```
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### HTML Drag and Drop API
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_Reading Files_
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The `dataTransfer` property of the `drop` event holds a list of `File` objects:
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```js
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/* suppress default behavior for drag and drop events */
function suppress(e) { e.stopPropagation(); e.preventDefault(); }
/* handle data from drop event */
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async function handleDropAsync(e) {
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suppress(e);
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/* get first file */
const f = e.dataTransfer.files[0];
/* get raw data */
const data = await f.arrayBuffer();
/* data is an ArrayBuffer */
const wb = XLSX.read(data);
/* do something with the workbook here */
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console.log(XLSX.utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]]));
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}
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drop_dom_element.addEventListener("drop", handleDropAsync, false);
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drop_dom_element.addEventListener("dragover", suppress, false);
drop_dom_element.addEventListener("dragenter", suppress, false);
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```
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### File System Access API
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:::warning Limited Browser Support
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At the time of writing, browser support was fairly limited. Chrome introduced
the feature in version 86. Safari did not support File System Access API.
:::
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:::caution pass
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When this demo was last tested, Google Chrome did not add an entry to the
"Downloads" list. Nevertheless the actual file was written correctly.
:::
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:::note Tested Deployments
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This browser demo was tested in the following environments:
| Browser | Date |
|:------------|:-----------|
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| Chrome 122 | 2024-04-07 |
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Some lesser-used browsers do not support File System Access API:
| Browser | Date |
|:------------|:-----------|
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| Safari 17.4 | 2024-04-07 |
| Firefox 124 | 2024-04-07 |
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:::
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<details><summary><b>Live Example</b> (click to show) </summary>
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This live example reads a file then tries to save as XLSX. If the File System
Access API is not supported, the result will be a clear message.
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```jsx live
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function SheetJSRoundTripFileSystemAPI() { return window.showSaveFilePicker ? (
<button onClick={async () => {
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/* Show picker and get data */
const [rFile] = await window.showOpenFilePicker({
types: [{
description: 'Spreadsheets',
accept: { 'application/vnd.ms-excel': ['.xlsx', '.xls', '.xlsb', /*...*/] }
}],
excludeAcceptAllOption: true,
multiple: false
});
const ab = await (await rFile.getFile()).arrayBuffer();
/* parse */
const wb = XLSX.read(ab);
/* Show picker and get handle to file */
const wFile = await window.showSaveFilePicker({
suggestedName: "SheetJSRT.xlsx",
types: [ { description: 'XLSX', accept: { 'application/vnd.ms-excel': ['.xlsx'] } } ]
});
const wstream = await wFile.createWritable();
/* write */
const buf = XLSX.write(wb, { bookType: "xlsx", type: "buffer" });
wstream.write(buf);
/* close stream to commit file */
wstream.close();
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}}>Click to read then save as XLSX</button>
) : ( <b>This browser does not support File System Access API</b> ); }
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```
</details>
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_Reading Files_
`window.showOpenFilePicker` shows a file picker and resolves to an array of
file handles. When `multiple: false` is set, the array has one element.
The `getFile` method resolves to a `File` object whose data can be read with
the `arrayBuffer` method:
```js
/* Show picker and get data */
const [hFile] = await window.showOpenFilePicker({
types: [{
description: 'Spreadsheets',
accept: { 'application/vnd.ms-excel': ['.xlsx', '.xls', '.xlsb', /*...*/] }
}],
excludeAcceptAllOption: true,
multiple: false
});
const ab = await (await hFile.getFile()).arrayBuffer();
/* parse */
const wb = XLSX.read(ab);
/* do something with the workbook */
console.log(XLSX.utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]]));
```
_Writing Files_
`window.showSaveFilePicker` shows a file picker and resolves to a file handle.
The `createWritable` method resolves to a `FileSystemWritableFileStream`, which
readily accepts `Uint8Array` data from `XLSX.write`:
```js
/* Show picker and get handle to file */
const hFile = await window.showSaveFilePicker({
suggestedName: "SheetJS.xlsx",
types: [
{ description: 'Excel 2007+ (XLSX)', accept: { 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet': ['.xlsx'] } },
{ description: 'Excel 97-2004 (XLS)', accept: { 'application/vnd.ms-excel': ['.xls'] } },
{ description: 'Excel 2007+ Binary (XLSB)', accept: { 'application/vnd.ms-excel.sheet.binary.macroEnabled.12': ['.xlsb'] } },
/* note that each MIME type must be unique! */
]
});
const wstream = await hFile.createWritable();
/* get extension */
const ext = hFile.name.slice(hFile.name.lastIndexOf(".")+1)
/* write */
wstream.write(XLSX.write(wb, { bookType: ext, type: "buffer" }))
/* close stream to commit file */
wstream.close();
```
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### File and Directory Entries API
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:::caution Deprecated
In the web browser, the File and Directory Entries API has been deprecated and
is not recommended for new applications.
`cordova-plugin-file` still uses the API patterns.
:::
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_Writing Files_
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The API is callback-based. At a high level:
1) `window.requestFileSystem` requests access to the filesystem. The callback
receives a `FileSystem` object.
2) A file is created using the `getFile` method. The callback receives a
`FileSystemFileEntry` object representing the file.
3) A writer is created using the `createWriter` method of the file object. The
callback receives a `FileWriter` object representing a file handle for writing.
4) Data is written using the `write` method of the `FileWriter` object. Unlike
the other methods, callbacks are attached to the `FileWriter` object directly.
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```js
// Request File System Access
window.requestFileSystem(window.PERSISTENT, 0, (fs) => {
// Request a handle to "SheetJS.xlsx", making a new file if necessary
fs.root.getFile("SheetJS.xlsx", {create: true}, entry => {
// Request a FileWriter for writing data
entry.createWriter(writer => {
// The FileWriter API needs an actual Blob
const u8 = XLSX.write(wb, { type: "buffer", bookType: "xlsx" });
const data = new Blob([u8], { type: "application/vnd.ms-excel" });
// `onwriteend` is called on success, `onerror` called on error
writer.onwriteend = () => {}; writer.onerror = () => {};
// write the data
writer.write(data);
});
});
});
```
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### Internet Explorer
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Internet Explorer offered proprietary APIs that were not adopted by Chromium.
#### Blob API
_Writing Files_
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IE10 and IE11 support `navigator.msSaveBlob`. `XLSX.writeFile` will use this
method if it is available.
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<details><summary><b>Implementation Details</b> (click to show)</summary>
**`XLSX.writeFile(wb, "SheetJS.xlsx");`** is roughly equivalent to:
```js
/* write data -- `writeFile` infers bookType from filename but `write` cannot */
const u8 = XLSX.write(wb, { bookType: "xlsx", type: "buffer" });
/* create Blob */
const blob = new Blob([u8]);
/* call msSaveBlob */
navigator.msSaveBlob(blob, "SheetJS.xlsx");
```
</details>
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#### VBScript
_Reading and Writing Files_
Internet Explorer 6-9 with VBScript support `Scripting.FileSystemObject`. This
is not supported in modern browsers.
This approach is implemented in the library `readFile` and `writeFile` methods.
It requires the shim script to be loaded before the main library script:
```html
<!-- load the shim script first -->
<script src="shim.min.js"></script>
<!-- then load the main script -->
<script src="xlsx.full.min.js"></script>
```
## Other Platforms
### NodeJS
`fs.readFileSync` and `fs.writeFileSync` allow for reading and writing files.
When using `require`, these are supported in `readFile` and `writeFile`:
```js
var XLSX = require("xlsx");
var wb = XLSX.readFile("sheetjs.numbers");
XLSX.writeFile(wb, "sheetjs.xls");
```
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[Installation](/docs/getting-started/installation/nodejs) has a special note for
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use with NodeJS ECMAScript Modules:
```js
import { readFile, writeFile, set_fs } from 'xlsx';
import * as fs from 'fs';
set_fs(fs);
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var wb = readFile("sheetjs.numbers");
writeFile(wb, "sheetjs.xlsx");
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```
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<details><summary><b>Implementation Details</b> (click to show)</summary>
**`XLSX.readFile(filepath)`** is equivalent to:
_CommonJS_
```js
var fs = require("fs");
var buf = fs.readFileSync(filepath);
var wb = XLSX.read(buf);
```
_ECMAScript Modules_
```js
import { read } from "xlsx";
import { readFileSync } from "fs";
var buf = readFileSync(filepath);
var wb = read(buf);
```
**`XLSX.writeFile(wb, filepath)`** is equivalent to:
_CommonJS_
```js
var fs = require("fs"), path = require("path");
var buf = XLSX.write(wb, { bookType: path.extname(filepath).slice(1), type: "buffer" });
fs.writeFileSync(filepath, buf);
```
_ECMAScript Modules_
```js
import { write } from "xlsx";
import { writeFileSync } from "fs";
import { extname } from "path";
var buf = write(wb, { bookType: extname(filepath).slice(1), type: "buffer" });
writeFileSync(filepath, buf);
```
</details>
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### ExtendScript
In Photoshop and other Adobe apps, `readFile` and `writeFile` use the `File`
object under the hood:
```js
#include "xlsx.extendscript.js"
var wb = XLSX.readFile("sheetjs.xlsx");
XLSX.writeFile(wb, "sheetjs.csv");
```
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The [ExtendScript demo](/docs/demos/extensions/extendscript) also covers "Common
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Extensibility Platform" (CEP) and "Unified Extensibility Platform" (UXP) details.
### Chrome Extensions
In Manifest v2 Chrome extensions, `writeFile` calls `chrome.downloads.download`.
This approach uses `URL.createObjectURL`, an API that is not supported in a
Manifest v3 Background Service Worker. For small exports, raw Base64 URLs can be
generated and downloaded.
The [Chromium demo](/docs/demos/extensions/chromium) covers the details.
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### Deno
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`readFile` uses `Deno.readFileSync` and `writeFile` uses `Deno.writeFileSync`:
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<CodeBlock language="ts">{`\
// @deno-types="https://cdn.sheetjs.com/xlsx-${current}/package/types/index.d.ts"
import * as XLSX from 'https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs';
\n\
const wb: XLSX.WorkBook = XLSX.readFile("sheetjs.numbers");
XLSX.writeFile(wb, "sheetjs.xlsx");`}
</CodeBlock>
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:::caution Deno entitlements
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Any Deno script using `XLSX.readFile` requires the `--allow-read` entitlement.
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Any Deno script using `XLSX.writeFile` requires the `--allow-write` entitlement.
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:::
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<details><summary><b>Implementation Details</b> (click to show)</summary>
**`XLSX.readFile(filepath)`** is equivalent to:
_ECMAScript Modules_
<CodeBlock language="ts">{`\
// @deno-types="https://cdn.sheetjs.com/xlsx-${current}/package/types/index.d.ts"
import * as XLSX from 'https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs';
\n\
const u8: Uint8Array = Deno.readFileSync(filepath);
const wb: XLSX.WorkBook = XLSX.read(u8);`}
</CodeBlock>
**`XLSX.writeFile(wb, filepath)`** is equivalent to:
_ECMAScript Modules_
<CodeBlock language="ts">{`\
// @deno-types="https://cdn.sheetjs.com/xlsx-${current}/package/types/index.d.ts"
import * as XLSX from 'https://cdn.sheetjs.com/xlsx-${current}/package/xlsx.mjs';
\n\
const u8 = XLSX.write(wb, { bookType: filepath.slice(filepath.lastIndexOf(".")+1), type: "buffer" });
Deno.writeFileSync(filepath, u8);`}
</CodeBlock>
</details>
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### Bun
Bun requires the `fs` module:
```js
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import { readFile, writeFile, set_fs } from 'xlsx';
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import * as fs from 'fs';
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set_fs(fs);
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var wb = readFile("sheetjs.numbers");
writeFile(wb, "sheetjs.xlsx");
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```
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The implementation is identical to [NodeJS ECMAScript Modules](#nodejs).
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### Apps
Desktop and mobile apps have their own specific APIs covered in separate demos:
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- [Electron and other desktop apps](/docs/demos/desktop)
- [React Native and other mobile apps](/docs/demos/mobile)
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[^1]: See ["Input Type" in "Reading Files"](/docs/api/parse-options#input-type)
[^2]: See ["Supported Output Formats" type in "Writing Files"](/docs/api/write-options#supported-output-formats)
[^3]: See ["Buffers and TypedArrays"](https://nodejs.org/api/buffer.html#buffers-and-typedarrays) in the NodeJS documentation.