userscripts/visual/4c-image-expander.js

// ==UserScript==
// @name        4c-image-expander
// @description General media expander
// @namespace   Violentmonkey Scripts
// @match       *://boards.4chan*.org/*/thread/*
// @exclude     *://boards.4chan*.org/*/catalog
// @version     1.0
// ==/UserScript==

window.toggleImgs = () => {
    const data = document.getElementsByClassName("fileThumb")

    for (let i = 0; i < data.length; ++i) {
        let img_data = data[i].getElementsByTagName("img")
        if (img_data[0].className === "fileDeletedRes retina") {
            continue
        } else if (img_data.length === 1) {
            ImageExpansion.expand(img_data[0])
        } else {
            ImageExpansion.contract(img_data[1])
        }
    }
}

const parentElem = document.getElementsByClassName("navLinks desktop")[0]
parentElem.innerHTML += " [<a href='javascript:toggleImgs()'>Toggle</a>]"