function isValid(ccnum){ var sum = 0; ccnum = ccnum.split(''); for(var i=0; i < ccnum.length; i++){ if(ccnum[i] == ' '){ ccnum.splice(i,1); } } for(var t = 0; t < ccnum.length; t=t+2){ ccnum[t] == ccnum[t]*2; } for(var w = 0; w < ccnum.length; w++){ sum = sum + Number(ccnum[w]); } if(sum % 10 === 0){ return true; }else{ return false; } } console.log(isValid("4408 0412 3456 7893") === false) console.log(isValid("5000000000000000") === false)