Check element is in viewport - jQuery plugin

onScreen.js

/**
 * $.onScreen jQuery plugin
 * @uses $("#eample").onScreen() // return true if element is in current view port
 */
$.fn.onScreen = function(x, y){
    if(x == null || typeof x == 'undefined') x = 1;
    if(y == null || typeof y == 'undefined') y = 1;
    var win = $(window);
    var viewport = {
        top : win.scrollTop(),
        left : win.scrollLeft()
    };

    viewport.right = viewport.left + win.width();
    viewport.bottom = viewport.top + win.height();
    
    var height = this.outerHeight();
    var width = this.outerWidth();

    if(!width || !height){
        return false;
    }
    
    var bounds = this.offset();
    bounds.right = bounds.left + width;
    bounds.bottom = bounds.top + height;
    
    var visible = (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));
    
    if(!visible){
        return false;   
    }
    var deltas = {
        top : Math.min( 1, ( bounds.bottom - viewport.top ) / height),
        bottom : Math.min(1, ( viewport.bottom - bounds.top ) / height),
        left : Math.min(1, ( bounds.right - viewport.left ) / width),
        right : Math.min(1, ( viewport.right - bounds.left ) / width)
    };
    return (deltas.left * deltas.right) >= x && (deltas.top * deltas.bottom) >= y;
};