Progressive image loader + infinite scroll

tumblr_loader.js

(function (win) {
    'use strict';

    var doc = win.document,
        scrollTop,
        pagination = doc.getElementsByClassName('pagination')[0],
        loadingPosts = false,
        xhr = new win.XMLHttpRequest(),
        page = 1,
        nextHref = win.location.href + (win.location.pathname === '/' ? '' : '/') + 'page/';
    
    if (pagination !== undefined) {
        pagination.parentNode.removeChild(pagination);
    }

    function loadHighRes() {

        var imgs = doc.querySelectorAll('[data-async]'),
            i = imgs.length,
            img;

        while (i) {
            img = imgs[i -= 1];

            img.onload = function () {
                this.removeAttribute('width');
                this.removeAttribute('height');
                this.removeAttribute('data-async');
            };

            img.src = img.dataset.async;

            if (img.complete) {
                img.onload();
                img.onload = null;
            }
        }
    }

    function loadPosts() {

        if (loadingPosts) { return; }

        loadingPosts = true;

        xhr.open('GET', nextHref + (page += 1), true);
        xhr.send();
    }

    function checkScroll() {

        scrollTop = (win.pageYOffset || doc.documentElement.scrollTop || 0);

        if (doc.height - (win.innerHeight + scrollTop) < win.innerHeight * 2) {
            loadPosts();
        }
    }

    xhr.onload = function () {

        if (this.status !== 200) { return; }

        var response = this.response.replace(/(\s\s)+/g, ' '),
            articles = response.match(/<article>(.*?)<\/article>/ig);

        if (articles && articles.length > 0) {
            doc.body.innerHTML += articles.join('');
            loadHighRes();
            loadingPosts = false;
        }
    };

    win.addEventListener('resize', checkScroll);
    win.addEventListener('scroll', checkScroll);
    win.addEventListener('load', loadHighRes);

}(this));