---
title: "loadAsync(data [, options])"
layout: default
section: api
---

Read an existing zip and merge the data in the current JSZip
object at the current folder level. This technique has some limitations, see
[here]({{site.baseurl}}/documentation/limitations.html).
If the JSZip object already contains entries, new entries will be merged. If
two have the same name, the loaded one will replace the other.

__Returns__ : A [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) with the updated zip object.
The promise can fail if the loaded data is not valid zip data or if it
uses unsupported features (multi volume, password protected, etc).

__Since__: v3.0.0

## Arguments

name               | type   | description
-------------------|--------|------------
data               | String/Array of bytes/ArrayBuffer/Uint8Array/Buffer/Blob/Promise | the zip file
options            | object | the options to load the zip file

Content of `options` :

name                          | type    | default | description
------------------------------|---------|---------|------------
options.base64                | boolean | false   | set to `true` if the data is base64 encoded, `false` for binary. [More](#base64-option).
options.checkCRC32            | boolean | false   | set to `true` if the read data should be checked against its CRC32. [More](#checkcrc32-option).
options.optimizedBinaryString | boolean | false   | set to `true` if (and only if) the input is a string and has already been prepared with a 0xFF mask.
options.createFolders         | boolean | false   | set to `true` to create folders in the file path automatically. Leaving it false will result in only virtual folders (i.e. folders that merely represent part of the file path) being created. [More](#createfolders-option).
options.decodeFileName        | function | decode from UTF-8 | the function to decode the file name / comment. [More](#decodefilename-option).

You shouldn't update the data given to this method : it is kept as it so any
update will impact the stored data.

Zip features supported by this method :

* Compression (<code>DEFLATE</code> supported)
* zip with data descriptor
* ZIP64
* UTF8 in file name, UTF8 in file content

Zip features not (yet) supported :

* password protected zip
* multi-volume zip

### `base64` option

```js
var zip = new JSZip();
zip.loadAsync("UEsDBAoDAAAAAJxs8T...AAAAAA==", {base64: true});
```

### `checkCRC32` option

The `checkCRC32` option will load every files, compute the CRC32 value and
compare it against the saved value.
With larger zip files, this option can have a significant performance cost.

```js
// here, "bin" is a corrupted zip file

zip.loadAsync(bin)
.then(function (zip) {
    // will be called, even if content is corrupted
}, function (e) {
    // won't be called
});

zip.loadAsync(bin, {
    checkCRC32: true
})
.then(function (zip) {
    // won't be called
}, function (e) {
    // Error: Corrupted zip : CRC32 mismatch
});
```

### `createFolders` option

```js
// here, "bin" is zip file containing:
// folder1/folder2/folder3/file1.txt

zip.loadAsync(bin)
.then(function (zip) {
    console.log(zip.files);
    // folder1/folder2/folder3/file1.txt
});

// with createFolders: true, all folders will be created
zip.loadAsync(bin, {createFolders: true})
.then(function (zip) {
    console.log(zip.files);
    // folder1/
    // folder1/folder2/
    // folder1/folder2/folder3/
    // folder1/folder2/folder3/file1.txt
});
```

### `decodeFileName` option

A zip file has a flag to say if the filename and comment are encoded with UTF-8.
If it's not set, JSZip has **no way** to know the encoding used. It usually
is the default encoding of the operating system. Some extra fields can give
the unicode version of the filename/comment too (in that case, we use it).

If we can't find an UTF-8 encoded filename/comment, we use the `decodeFileName`
function (which is by default an UTF-8 decode).

The function takes the bytes array (Uint8Array or Array) and returns the
decoded string.

```js
// here, "bin" is a russian zip file, using the cp866 encoding for file names
// by default, using UTF-8 leads to wrong file names:
zip.loadAsync(bin)
.then(function (zip) {
    console.log(zip.files);
    // '����� �����/': ...
    // '����� �����/����� ⥪�⮢�� ���㬥��.txt': ...
});

// using the correct encoding solve the issue:
var iconv = require('iconv-lite');
zip.loadAsync(bin, {
  decodeFileName: function (bytes) {
    return iconv.decode(bytes, 'cp866');
  }
})
.then(function (zip) {
    console.log(zip.files);
    // 'Новая папка/': ...
    // 'Новая папка/Новый текстовый документ.txt': ...
});
```

## Other examples

```js
var zip = new JSZip();
zip.loadAsync(zipDataFromXHR);
```

```js
require("fs").readFile("hello.zip", function (err, data) {
  if (err) throw err;
  var zip = new JSZip();
  zip.loadAsync(data);
}
```

Using sub folders :

```js
// here, "bin" is zip file containing:
// file1.txt
// folder1/file2.txt

var zip = new JSZip();
zip.folder("subfolder").loadAsync(bin)
.then(function (zip) {
    // "zip" is still in the "subfolder" folder
    console.log(zip.files);
    // subfolder/file1.txt
    // subfolder/folder1/file2.txt
});
```

Using `loadAsync` multiple times:

```js
// here, "bin1" is zip file containing:
// file1.txt
// file2.txt
// and "bin2" is zip file containing:
// file2.txt
// file3.txt

var zip = new JSZip();
zip.loadAsync(bin1)
.then(function (zip) {
    return zip.loadAsync(bin2);
}).then(function (zip) {
    console.log(zip.files);
    // file1.txt, from bin1
    // file2.txt, from bin2
    // file3.txt, from bin2
});
```