javascript - TypeError: invalid 'in' operand a in a class -

have javascript code here uses jquery create class , use class functions then.

function sample(a, b) {     var id = a;     var img_src = b;      this.getid = function()     {         return id;     };      this.move = function(ptop, pleft)     {         var p = $(this).position();         var mov_top = p.top + ptop;         var mov_left = p.left + pleft;         $(this).animate({             top: mov_top,             left: mov_left         });     } } 

and calling when clicking button :

<button onclick="create(3);">click me :d</button>  <script>                 function create(id)     {         var mysample = new sample(id, 'url');         mysample.move(50, 50);     }    </script> 

and returns me error typeerror: invalid 'in' operand don't see comes from...

do has idea?

try passing this create() instead of 3 should a within sample() , setting button css position relative

function sample(a, b)  {      var id = a;      var img_src = b;        this.getid = function()      {          return id;      };        this.move = function(ptop, pleft)      {          var p = $(a).position();          var mov_top = p.top + ptop;          var mov_left = p.left + pleft;          $(a).animate({              top: mov_top,              left: mov_left          });      }  }

button {    position:relative;  }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js">  </script>  <button onclick="create(this);">click me :d</button>    <script>                  function create(id)      {          var mysample = new sample(id, 'url');          mysample.move(50, 50);      }     </script>