Add commas or spaces to group every three digits

Question

I have a function to add commas to numbers:

function commafy( num ) {
  num.toString().replace( /\\B(?=(?:\\d{3})+)$/g, \",\" );
}

Unfortun

Answer 1

Here you go edited after reading your comments.

function commafy( arg ) {
   arg += '';                                         // stringify
   var num = arg.split('.');                          // incase decimals
   if (typeof num[0] !== 'undefined'){
      var int = num[0];                               // integer part
      if (int.length > 4){
         int     = int.split('').reverse().join('');  // reverse
         int     = int.replace(/(\d{3})/g, "$1,");    // add commas
         int     = int.split('').reverse().join('');  // unreverse
      }
   }
   if (typeof num[1] !== 'undefined'){
      var dec = num[1];                               // float part
      if (dec.length > 4){
         dec     = dec.replace(/(\d{3})/g, "$1 ");    // add spaces
      }
   }

   return (typeof num[0] !== 'undefined'?int:'') 
        + (typeof num[1] !== 'undefined'?'.'+dec:'');
}