Get the whole document's html with JavaScript/JQuery

This will get you all the HTML:

document.documentElement.outerHTML

Unfortunately it does not return the doctype. But you can use document.doctype to get it and glue the two together.

You can do

new XMLSerializer().serializeToString(document);

for all browsers newer than IE 9

try this.

$("html").html()

document is a variable it dose not represent the html tag.

EDIT

To get the doctype one could use

document.doctype