Large String - 3,665 ops/sec
Small String - 1,162,858 ops/sec
window.atob(base64EncodedString)
Large String - 941 ops/sec
Small String - 2,137,575 ops/sec
base64Decode2(base64EncodedString)
Large String - 141 ops/sec
Small String - 351,977 ops/sec
base64Decode3(base64EncodedString)
https://github.com/dankogai/js-base64/blob/master/base64.js
Performed worse than the other 3
https://ctrlq.org/code/19920-encode-decode-base64-javascript
Untested
https://gist.github.com/stubbetje/229984
Untested
Quick and dirty way of getting a large string to encode and decode for testing.
var base64EncodedString = window.btoa(encodeURI(document.body.outerHTML))