New Window - Can't Read Property

I've code like this:

var x =window.open('http://localhost/canvas.html','myokno')
var w =x.width
Permission denied to get property Window.width
var w =x.innerWidth

Permission denied to get property Window.innerWidth
why i can get properties of new created window???
The second problem is much more important:
i want to get element which id is "canvas" and it is in new window so i do
like this:

var canvas = myokno.document.getElementById('canvas')
ReferenceError: myokno is not defined
var canvas = x.document.getElementById('canvas')
Permission denied to call method HTMLDocument.getElementById

so i start working on the problem and:
var can = x.document
can
[object HTMLDocument]
var can2 = can.getElementById('canvas')
Permission denied to call method HTMLDocument.getElementById

what i doing wrong?