wallet-core/node_modules/randomfill/README.md

randomfill

randomfill from node that works in the browser. In node you just get crypto.randomBytes, but in the browser it uses .crypto/msCrypto.getRandomValues

var randomFill = require('randomfill');
var buf
randomFill.randomFillSync(16);//get 16 random bytes
randomFill.randomFill(16, function (err, resp) {
  // resp is 16 random bytes
});