Simulate keypress usnig javascript (doesn't work in Safari or Chrome)

gistfile1.js

var elem = (document.getElementsByClassName('mentionsTextarea'))[0];
elem.value = 'www.youtube.com';
elem.blur();
elem.value += ' ';
var evt = document.createEvent('KeyboardEvent');
evt.initKeyEvent(
           'keypress', 
           true,     // key down events bubble 
           true,     // and they can be cancelled 
           null,     // Use the default view 
           false,        // ctrl 
           false,       // alt
           false,        //shift
           false,       //meta key 
           32,          // Space keycode, use 13 for Enter
           0
          );

elem.dispatchEvent(evt);