function sum(input){  
               
 if (toString.call(input) !== "[object Array]")  
    return false;  
        
            var total =  0;  
            for(var i=0;i<input.length;i++)  
              {                    
                if(isNaN(input[i])){  
                continue;  
                 }  
                  total += Number(input[i]);  
               }  
             return total;  
            }  
console.log(sum([1,2,3]));  
console.log(sum([100,-200,3]));  
console.log(sum([1,2,'a',3])); 