doubleNum.js

function doubleNum(num) {

  var 
    numStr = num + '',
    numLen = numStr.length;

  if (!(numLen%2)) {
    var
      first = numStr.substring(0, numLen/2),
      second = numStr.substring(numLen/2);

    if (first === second) return num; 
    else return num*2;
   }
  
   else return num*2;
  
}