jQuery check if element is visible in view port

isElementInViewport.js

function isElementInViewport (el) {

    if (typeof jQuery === "function" && el instanceof jQuery) {
        el = el[0];
    }

    var rect = el.getBoundingClientRect();

    return (
        (rect.top + rect.height) >= 0 &&
        rect.left >= 0 &&
        (rect.bottom - rect.height) <= (window.innerHeight || document.documentElement.clientHeight) && /*or $(window).height() */
        rect.right <= (window.innerWidth || document.documentElement.clientWidth) /*or $(window).width() */
    );

}

function onVisibilityChange(el, callback) {
    var old_visible;
    return function () {
        var visible = isElementInViewport(el);
        if (visible != old_visible) {
            old_visible = visible;
            if (typeof callback == 'function') {
                callback();
            }
        }
    }
}

function handler() {
    $('.elements').each(function(){
        console.log(isElementInViewport($(this)))
    });
}

$(window).on('DOMContentLoaded load resize scroll', handler);