Bonfire: Roman Numeral Converter

romanconverter.js

function convert(num) {  
    var x = '';
    [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1].map(
      function(obj,i){ 
        while (num>=obj){ 
          x+=['M','CM','D','CD','C','XC','L','XL','X','IX','V','IV','I'][i];
          num-=obj;}});
    return x;    
}
convert(36);  

Convert the given number into a roman numeral.
All roman numerals answers should be provided in upper-case.