How to simulate typing in input field using jQuery?

What I want is to simulate typing in <input> field using javascript.

I have the following code:

var press = jQuery.Event("keydown");
press.ctrlKey = false;
press.which = 65;
$("#test").trigger(press);

But when I load the page, the #test input field has no typed characters, the keycode of '65' represents 'A', but there is no 'A' input.

Basically what I want is to automatically typing in the website using Greasemonkey.

Please give me some ideas or some library with which I can use to do this.
Thanks a lot!