Download Binary Files with Javascript

Question

I want to download binary files using Javascript.

I have a REST service that returns the binary data and i want to know if its possible to show the binary file, whichever the file extension.

This is my current code:

var xhr = new XMLHttpRequest;
xhr.open("GET", requestUrl);
xhr.addEventListener("load", function () {
    var ret = [];
    var len = this.responseText.length;
    var byte;
    for (var i = 0; i < len; i++) {
        byte = (this.responseText.charCodeAt(i) & 0xFF) >>> 0;
        ret.push(String.fromCharCode(byte));
    }
    var data = ret.join('');
    data = "data:application/pdf;base64," + btoa(data);

    window.open(data, '_blank', 'resizable, width=1020,height=600');
}, false);

xhr.setRequestHeader("Authorization", "Bearer " + client.accessToken);
xhr.overrideMimeType("octet-stream; charset=x-user-defined;");
xhr.send(null);

Thanks!

you should check this answer: stackoverflow.com/questions/9620497/… — Doua Beri
– Doua Beri, Commented Jul 17, 2013 at 9:51
@JoDavid - No. I want to download any type of document. Images(png, jpeg, gif), documents (pdf, doc, txt), ... — nuno.filipesf
– nuno.filipesf, Commented Jul 17, 2013 at 9:59

Jo David · Accepted Answer · 2017-01-12 07:46:26Z

68

Have a look at the MDN article on XMLHttpRequest.

If you set the response of the XMLHttpRequest to ArrayBuffer you could do the following:

var xhr = new XMLHttpRequest();
xhr.open("GET", requestUrl);
xhr.responseType = "arraybuffer";

xhr.onload = function () {
    if (this.status === 200) {
        var blob = new Blob([xhr.response], {type: "application/pdf"});
        var objectUrl = URL.createObjectURL(blob);
        window.open(objectUrl);
    }
};
xhr.send();

Option 2:
You could use Blob as the response of the XMLHttpRequest. And then maybe save it in the FileSystem (FileSystem API)

It may look like:

var xhr = new XMLHttpRequest();
xhr.open("GET", requestUrl);
xhr.responseType = "blob";

xhr.onload = function () {
    onDownloaded(this);
};
xhr.send();

Option 3:
If you only want to download and "show" images you can easily do this like so:

var img = new Image();

// add the onload event before setting the src
img.onload = function() {
    onImageDownloaded(img);
}

// start the download by setting the src property
img.src = requestUrl

edited Jan 12, 2017 at 7:46

answered Jul 17, 2013 at 9:52

Jo David

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8 Comments

nuno.filipesf Over a year ago

Thanks for the answer. But my problem is a bit different. I can download pdfs or images, but when i call the REST service that returns the binary data, i don't know what is the type of the file.

Jo David Over a year ago

You could make another request just before downloading the file to get the fileType and maybe the file name (for the UI).

Akash Kava Over a year ago

why would you not use content-type header instead of hard coding type as application/pdf?

Maxim Over a year ago

A tiny correction Jo, for a bytearray Brob parameter should be an array. ...new Blob([xhr.response], {type: 'application/pdf'});

Arup Rakshit Over a year ago

Where the function onDownloaded is defined?

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