Get window viewport width and height

GetViewPort.js

/**
 * Get window viewport width
 * @param side {string} - (width|height|both)
 *
 * Usage getViewPort('width'); // return viewport width
 */
function getViewPort(side){
    var side = side || 'both';
    var viewport = { width: 0, height: 0 };

    if (typeof window.innerWidth != 'undefined') {
        viewport.width  = window.innerWidth;
        viewport.height = window.innerHeight;
    }
    // IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
    else if (typeof document.documentElement != 'undefined' && typeof document.documentElement.clientWidth != 'undefined' && document.documentElement.clientWidth != 0) {
        viewport.width  = document.documentElement.clientWidth;
        viewport.height = document.documentElement.clientHeight;
    }
    // older versions of IE
    else {
        viewport.width  = document.getElementsByTagName('body')[0].clientWidth;
        viewport.height = document.getElementsByTagName('body')[0].clientHeight;
    }

    switch(side){
        case 'width':
            return viewport.width;
            break;
        case 'height':
            return viewport.height;
            break;
        case 'both':
            return viewport;
            break;
    }
}