getDocumentDimensions.js

var getDocumentDimensions = function () {
    return {
        width: Math.max(
            document.body.scrollWidth, document.documentElement.scrollWidth,
            document.body.offsetWidth, document.documentElement.offsetWidth,
            document.body.clientWidth, document.documentElement.clientWidth
        ),
        height: Math.max(
            document.body.scrollHeight, document.documentElement.scrollHeight,
            document.body.offsetHeight, document.documentElement.offsetHeight,
            document.body.clientHeight, document.documentElement.clientHeight
        )
    };
};