CoffeeScriptで日本語の桁区切り (例 123456789 -> 1億2345万6789) #CoffeeScript

CoffeeScriptで数字を
1億2345万6789
などと日本語の桁区切りで表示する関数 Beautify.jpn です。

beautify.coffee

class Beautify
    @jpn: (val) ->
        unit = ['', '万', '億', '兆', '京', '垓']
        num_arr = String(val).replace(/(\d)(?=(\d\d\d\d)+$)/g, "$1,").split(",").reverse()
        num_arr2 = (
            num.replace(/^[0]+/g, '') + (if num is "0000" then "" else unit[i]) for num, i in num_arr
            )
        return (
            num_arr2.reverse().toString().replace(/,/g, '')
            )

console.log Beautify.jpn(123456789) # 1億2345万6789
console.log Beautify.jpn(120000789) # 1億6789