ArrayBuffer to base64 encoded string

I need an efficient (read native) way to convert an ArrayBuffer to a base64 string which needs to be used on a multipart post.

Solution 1:

function _arrayBufferToBase64( buffer ) {
    var binary = '';
    var bytes = new Uint8Array( buffer );
    var len = bytes.byteLength;
    for (var i = 0; i < len; i++) {
        binary += String.fromCharCode( bytes[ i ] );
    }
    return window.btoa( binary );
}

but, non-native implementations are faster e.g. https://gist.github.com/958841 see http://jsperf.com/encoding-xhr-image-data/6

Solution 2:

This works fine for me:

var base64String = btoa(String.fromCharCode.apply(null, new Uint8Array(arrayBuffer)));

In ES6, the syntax is a little simpler:

const base64String = btoa(String.fromCharCode(...new Uint8Array(arrayBuffer)));

As pointed out in the comments, this method may result in a runtime error in some browsers when the ArrayBuffer is large. The exact size limit is implementation dependent in any case.