Plain Code

function getViewportHeight() {
    var height = self.innerHeight; // Safari, Opera
    var mode = document.compatMode;

    if ( (mode || $.browser.msie) && !$.browser.opera ) { // IE, Gecko
        height = (mode == 'CSS1Compat') ?
        document.documentElement.clientHeight : // Standards
        document.body.clientHeight; // Quirks
    }
    
    return height;
}

function getViewportWidth() {
    var width = self.innerWidth; // Safari, Opera
    var mode = document.compatMode;

    if ( (mode || $.browser.msie) && !$.browser.opera ) { // IE, Gecko
        width = (mode == 'CSS1Compat') ?
        document.documentElement.clientWidth : // Standards
        document.body.clientWidth; // Quirks
    }

    return width;
}