Write a JavaScript program to create a new string from a given string taking the last 3 characters and added at both the front and back. The string length must be 3 or more

function front_back3(str)
 {
  if (str.length>=3)
   {
   str_len = 3;
 
  back = str.substring(str.length-3);
   return back + str + back;
 }
   else
     return false;
 }
console.log(front_back3("abc"));
console.log(front_back3("ab"));
console.log(front_back3("abcd"));