Convert Javascript UTF-8 to ASCII (like Iconv('UTF-8', 'ASCII//TRANSLIT', $string) in PHP)

The easiest way I've found:

var str = "üó";
var combining = /[\u0300-\u036F]/g; 

console.log(str.normalize('NFKD').replace(combining, ''));

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize

As @Pointy said, your only option is to map/replace characters according to a dictionary.

You'll find this really useful: https://github.com/backbone-paginator/backbone.paginator/blob/a579796a30e583c4dfa09e0a86e4abd21e0b5b56/plugins/diacritic.js