Why this one does not work? Simulate a mouse event

Hi I m trying to simulate a mouse event but is seems to not work. here is the code thata Iam using for testing

Everithing goes fine until it reraches  line number 5. in the console says dispatchEvent is  undefined

var win = new Window("dialog","testerWindow",[200,200,400,400]);

win.onClick=  function(){alert("Hello World")}

var event = ScriptUI.events.createEvent("MouseEvent");

var init = event.initMouseEvent("click",true,true,1,win,0,0,0,0,0,1);

win.dispatchEvent(init);

win.show()

it should show an alert Message as soon as the window shows up right?