JavaScript function that determines if an element is in the window's viewport

element-inviewport.js

var IsInViewport = (function () {
    "use strict";

    var func;

    func = function (el, par) {
        var ret, elRect, parRect;
        elRect = el.getBoundingClientRect();
        if (par) {
            parRect = par.getBoundingClientRect();
        } else {
            parRect = {
                top: 0,
                left: 0,
                bottom: (window.innerHeight || document. documentElement.clientHeight),
                right: (window.innerWidth || document. documentElement.clientWidth)
            };
        }
        ret = (
            elRect.top >= parRect.top &&
            elRect.left >= parRect.left &&
            elRect.bottom <= parRect.bottom &&
            elRect.right <= parRect.right
        );
        return ret;
    };

    return func;
}());