Convert base64 string to ArrayBuffer

Question

Try this:

function _base64ToArrayBuffer(base64) {
    var binary_string = window.atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = binary_string.charCodeAt(i);
    }
    return bytes.buffer;
}

Using TypedArray.from:

Uint8Array.from(atob(base64_string), c => c.charCodeAt(0))

Performance to be compared with the for loop version of Goran.it answer.

Goran.it's answer does not work because of unicode problem in javascript - https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding.

I ended up using the function given on Daniel Guerrero's blog: http://blog.danguer.com/2011/10/24/base64-binary-decoding-in-javascript/

Function is listed on github link: https://github.com/danguer/blog-examples/blob/master/js/base64-binary.js

Use these lines

var uintArray = Base64Binary.decode(base64_string);  
var byteArray = Base64Binary.decodeArrayBuffer(base64_string); 

Just found base64-arraybuffer, a small npm package with incredibly high usage, 5M downloads last month (2017-08).

https://www.npmjs.com/package/base64-arraybuffer

For anyone looking for something of a best standard solution, this may be it.

For Node.js users:

const myBuffer = Buffer.from(someBase64String, 'base64');

myBuffer will be of type Buffer which is a subclass of Uint8Array. Unfortunately, Uint8Array is NOT an ArrayBuffer as the OP was asking for. But when manipulating an ArrayBuffer I almost always wrap it with Uint8Array or something similar, so it should be close to what's being asked for.