[zebra]

var str = '1-2;2-450;3-16;4-73;5-21;', arr, i = 0, len, numbers;
arr = str.split(';');
len = arr.length;
console.log(arr);
for(; i < len; i +=1) {
   numbers = arr[i].split('-');
   if(numbers) {
     alert(numbers.join(','));
   }
}