Cray-z with Terniaries!!

// taken from http://www.dreamincode.net/code/snippet154.htm
//
// Find the weaknesses, and clean up the code.
// Find at least 3 things you can make better!
//
// Test numbers (return true):
// 4111111111111111
// 378282246310005
// 5555555555554444

//This solution is called "Cray-z with Terniaries!!!!1"

function isCreditCard( CC ) {
     if (CC.length > 19)
          return (false);

     var sum = 0,
 		 mul = 1, 
		 len = CC.length;  //Variables were going to window.scope. Now local to function
		
     for (i = 0; i < len; i++) // is there value in abstracting "for" logic here?
     {
          var digit = CC.substring(len-i-1,len-i),
          	  tproduct = parseInt(digit ,10)*mul;  //Same variable combination with var declaration.  Now I'm wondering if this is stylistic...
        
			sum +=(tproduct >= 10)?(tproduct % 10) + 1:(sum += tproduct); //hopefully improved readability by reducing to terniary operator
		  	mul+=(mul==1)?1:-1;	          
     }
     
	return ((sum % 10) == 0)?true:false;	
}