fade-in-elements-when-visited-firsttime.js

document.addEventListener('DOMContentLoaded', function() {
    if (calledWithin(60)) {
        return;
    }
    var elems = document.getElementsByClassName('fadein-firsttime');
    for (var i = 0; i < elems.length; i++) {
        (function() {
            var elem = elems.item(i);
            elem.style.transition = '';
            elem.style.opacity = 0;
            window.addEventListener('load', function() {
                var duration = elem.getAttribute('data-duration');
                duration = duration || '1s';
                elem.style.transition = 'opacity ' + duration;
                elem.style.opacity = 1;
            });
        })();
    }

    function calledWithin(seconds) {
        var now = new Date().getTime();
        var storage = window.sessionStorage;
        try {
            var last = parseInt(storage.getItem('last-called'));
            storage.setItem('last-called', now);
            return (now < last + seconds * 1000);
        }
        catch (e) {
            return false;
        }
    }
});