Convert English number to Bangla in Javascript

js-en-to-bn.js

var bnNumbers = {
    '0': '০',
    '1': '১',
    '2': '২',
    '3': '৩',
    '4': '৪',
    '5': '৫',
    '6': '৬',
    '7': '৭',
    '8': '৮',
    '9': '৯'
};

String.prototype.getBnDigit = function () {
    var str = this;
    for (var x in bnNumbers) {
        str = str.replace(new RegExp(x, 'g'), bnNumbers[x]);
    }
    return str;
};

var enNumber = "1234";

console.log(enNumber.getBnDigit());