javascript - I have Copied Below code but its not working in my application. Why? -

this code have copied here stack overflow not working in application working in jsfiddle. not performing action in application.

<textarea name="comment_text" id="comment_text"  class="post_description_text"></textarea>  $(".post_description_text").keydown(function(e){      if (e.keycode == 13 && !e.shiftkey){            e.preventdefault();return false;      }    });