rand = function(min, max) {  
  if (min==null && max==null)  
    return 0;      
    
  if (max == null) {  
      max = min;  
      min = 0;  
    }  
    return min + Math.floor(Math.random() * (max - min + 1));  
  };  
 console.log(rand(20,1));  
 console.log(rand(1,10));  
 console.log(rand(6));  
 console.log(rand());