ArrayBuffer to base64 encoded string

Question

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

Answer 1

This works fine for me:

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

In ES6, the syntax is a little simpler:

let 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.