generateAsync(options[, onUpdate])

Generates the complete zip file at the current folder level.

Returns : A Promise of the generated zip file.

An error will be propagated if the asked type is not available in the browser, see

Since: v3.0.0


name type default description
options object   the options to generate the zip file :
options.type string   The type of zip to return, see below for the other types. Required. More.
options.compression string STORE (no compression) the default file compression method to use. More.
options.compressionOptions object null the options to use when compressing the file. More.
options.comment string   The comment to use for the zip file. More.
options.mimeType string application/zip mime-type for the generated file. More.
options.platform string DOS The platform to use when generating the zip file. More.
options.encodeFileName function encode with UTF-8 the function to encode the file name / comment. More.
options.streamFiles boolean false Stream the files and create file descriptors, see below. More.
onUpdate function   The optional function called on each internal update with the metadata. More.

type option

Possible values for type :

  • base64: the result will be a string, the binary in a base64 form.
  • binarystring (or string, deprecated): the result will be a string in “binary” form, using 1 byte per char (2 bytes).
  • array: the result will be an Array of bytes (numbers between 0 and 255) containing the zip.
  • uint8array: the result will be a Uint8Array containing the zip. This requires a compatible browser.
  • arraybuffer: the result will be a ArrayBuffer containing the zip. This requires a compatible browser.
  • blob: the result will be a Blob containing the zip. This requires a compatible browser.
  • nodebuffer: the result will be a nodejs Buffer containing the zip. This requires nodejs.

Note : when using type = “uint8array”, “arraybuffer” or “blob”, be sure to check if the browser supports it (you can use

zip.generateAsync({type: "uint8array"}).then(function (u8) {
    // ...

compression and compressionOptions options

Available compression methods are STORE (no compression) and DEFLATE.

The compressionOptions parameter depends on the compression type. With STORE (no compression), this parameter is ignored. With DEFLATE, you can give the compression level with compressionOptions : {level:6} (or any level between 1 (best speed) and 9 (best compression)).

Note : if the entry is already compressed (coming from a compressed zip file), calling generateAsync() with a different compression level won’t update the entry. The reason is simple : JSZip doesn’t know how compressed the content was and how to match the compression level with the implementation we use.

    type: "blob",
    compression: "DEFLATE",
    compressionOptions: {
        level: 9

comment option

The zip format has no flag or field to give the encoding of this field and JSZip will use UTF-8. With non ASCII characters you might get encoding issues if the file archiver doesn’t use UTF-8 (or the given encoding) to decode the comment.

    type: "blob",
    comment: "The comment text for this zip file"

mimeType option

This field is used when you generate a Blob and need to change the mime type. Useful when you need to generate a file with a different extension, ie: “.ods”.

Note, this won’t change the content of the file, only the other programs may see it.

//This example will Generate a Open Document Spreadsheet, with the correct mime type
var zip = new JSZip();
zip.file("mimetype", "application/vnd.oasis.opendocument.spreadsheet");
var metaInf = zip.folder("META-INF");
metaInf.file("manifest.xml", "<...");
// ...

//Generate the file
    type: "blob",
    mimeType: "application/ods",
    compression: "DEFLATE"
}).then(function (odsFile) {
    // odsFile.type == "application/ods"

platform option

Possible values for platform : DOS and UNIX. It also accepts nodejs process.platform values. When using DOS, the attribute dosPermissions of each file is used. When using UNIX, the attribute unixPermissions of each file is used.

If you set the platform value on nodejs, be sure to use process.platform. fs.stats returns a non executable mode for folders on windows, if you force the platform to UNIX the generated zip file will have a strange behavior on UNIX platforms.

// on nodejs
zip.file(pathname, content, {
    date: stat.mtime,
    unixPermissions: stat.mode

// ...

    type: 'nodebuffer',
    platform: process.platform

encodeFileName option

By default, JSZip uses UTF-8 to encode the file names / comments. You can use this method to force an other encoding. Note: the encoding used is not stored in a zip file, not using UTF-8 may lead to encoding issues. The function takes a string and returns a bytes array (Uint8Array or Array).

See also decodeFileName on JSZip#loadAsync().

// using iconv-lite for example
var iconv = require('iconv-lite');

    type: 'uint8array',
    encodeFileName: function (string) {
        return iconv.encode(string, 'your-encoding');

streamFiles option

In a zip file, the size and the crc32 of the content are placed before the actual content: to write it we must process the whole file. When this option is false (the default) the processed file is held in memory. It takes more memory but generates a zip file which should be read by every program. When this options is true, we stream the file and use data descriptors at the end of the entry. This option uses less memory but some program might not support data descriptors (and won’t accept the generated zip file).

    type: 'uint8array',
    streamFiles: true

onUpdate callback

If specified, this function will be called each time a chunk is pushed to the output stream (or internally accumulated).

The function takes a metadata object which contains information about the ongoing process.

Metadata : the metadata are:

name type description
percent number the percent of completion (a double between 0 and 100)
currentFile string the name of the current file being processed, if any.
zip.generateAsync({type:"blob"}, function updateCallback(metadata) {
    console.log("progression: " + metadata.percent.toFixed(2) + " %");
    if(metadata.currentFile) {
        console.log("current file = " + metadata.currentFile);

Other examples

.then(function (content) {
    // see FileSaver.js
    saveAs(content, "");
.then(function (content) {
zip.folder("folder_1").folder("folder_2").file("hello.txt", "hello");
// zip now contains:
// folder_1/
// folder_1/folder_2/
// folder_1/folder_2/hello.txt

.then(function (content) {
    // relative to folder_1/, this file only contains:
    // folder_2/
    // folder_2/hello.txt
    require("fs").writeFile("", content, function(err){/*...*/});