I know this is kind of old but for someone looking for a better and newer solution please use the Crypto API and a SHA-256 or higher variant for the algorithm since MD5 has exploitable flaws.

var a = new FileReader();

a.readAsArrayBuffer(blob);

a.onloadend = function () {

  let hashPromise = crypto.subtle.digest(SHA-256, a.result);// it outputs a promise

};