Convert a Number to it's bengali number representation

bengali-digit-converter.js

function toBengaliNumber(number) {
    var numbers = {
    '1': '১',
    '2': '২',
    '3': '৩',
    '4': '৪',
    '5': '৫',
    '6': '৬',
    '7': '৭',
    '8': '৮',
    '9': '৯',
    '0': '০'
};
    if(typeof number !== 'undefined' && !isNaN(number)) {
        var numericText = Number(number).toString();
      return numericText.split('').reduce(function(a,b) {
            return (b in numbers) ? a += numbers[b] : a += b;
        }, '');
    } else {
        throw new Error('Expected valid number but found ', number);
    }
}

var banglaNumber = toBengaliNumber('56');
console.log("Now the number is :", banglaNumber);