text: //var a = new Array(5,"5",3,false,4,5,undefined,9)
  //a.lastIndexOf(5);
  5
  //a.lastIndexOf(5, 1);
  0
  //a.lastIndexOf(5, 2);
  0
  //a.lastIndexOf(5, 6);
  5
  //a.lastIndexOf(5, 10);
  5
  //a.lastIndexOf(true);
  -1
  //a.lastIndexOf(undefined);
  6
  //a.lastIndexOf("5");
  1
  