ViewFullSizeInstagramPhotos.user.js

// ==UserScript==
// @name         View Full Size Instagram Photos
// @description  Clicking an Instagram photo opens the full size image
// @version      1.0.9
// @author       heavyLobster2
// @namespace    github.com/heavyLobster2
// @downloadURL  https://gist.github.com/heavyLobster2/fb8c960748e205c15266/raw/ViewFullSizeInstagramPhotos.user.js
// @match        *://www.instagram.com/*
// @grant        none
// ==/UserScript==
(function () {
    "use strict";
    
    function procImage(image) {
        if (typeof image.dataset.processed === "undefined" && image.src !== "") {
            var link = document.createElement("a");
            link.href = image.src;
            link.className = image.className;
            
            var container = image.parentNode;
            container.replaceChild(link, image);
            link.appendChild(image);
            
            hideSiblings(container);
            
            image.dataset.processed = "";
        } else {
            hideSiblings(image.parentNode.parentNode);
        }
    }
    
    function hideSiblings(element) {
        var siblings = element.parentNode.childNodes;
        for (var i = 0; i < siblings.length; i++) {
            if (siblings[i] !== element && siblings[i] instanceof Element) {
                if (siblings[i].style.display !== "none") siblings[i].style.display = "none";
            }
        }
    }
    
    function procImages(images) {
        var allImages = document.querySelectorAll("img.FFVAD");
        for (var i = 0; i < allImages.length; i++) {
            procImage(allImages[i]);
        }
    }
    
    procImages();
    
    var observer = new MutationObserver(function (mutations) {
        procImages();
    });
    observer.observe(document, { subtree: true, childList: true });
})();