capture d'écran à l'aide de html2canvas

Je fais appel screenView() d'une autre classe. Je suis capable de l'appeler mais je ne suis pas arriver strDataURI. Ce que je fais mal?

       function screenView(){
var image;
var date = new Date();
var message,
timeoutTimer,
timer;
var proxyUrl = "http://html2canvas.appspot.com";
var iframe,d;
$(this).prop('disabled',true);
var url = "http://www.facebook.com/google";
var urlParts = document.createElement('a');
urlParts.href = url;
$.ajax({
data: {
xhr2:false,
url:urlParts.href
},
url: proxyUrl,
dataType: "jsonp",
success: function(html){
iframe = document.createElement('iframe');
$(iframe).css({
'visibility':'hidden'
}).width($(window).width()).height($(window).height());
$('#content').append(iframe);
d = iframe.contentWindow.document; 
alert("d-----"+d);
d.open();
$(iframe.contentWindow).unbind('load');
alert("inside>>"+ $(iframe).contents().find('body'));
$(iframe).contents().find('body').html2canvas({
canvasHeight: d.body.scrollHeight,
canvasWidth: d.body.scrollWidth,
logging:true
}); 
alert("inside before load view");
$(iframe.contentWindow).load(function(){
alert("inside view");
$(iframe).contents().find('body').html2canvas({
canvasHeight: 30,
canvasWidth: 10,
logging:true,
proxyUrl: proxyUrl,
logger:function(msg){
$('#logger').val(function(e,i){
return i+"\n"+msg;
});
},
ready: function(renderer) {
alert("in side ready renderer");
$('button').prop('disabled',false);
$("#content").empty();               
var finishTime = new Date();
var strDataURI = renderer.canvas.toDataURL("image/jpeg"); 
image = strDataURI
alert("last"+strDataURI);
d.close();
}
});
});
}
});
return image;
}