A very basic user script to inline images in Twitch chat.

twitchinlineimages.js

// ==UserScript==
// @name         TwitchInlineImages
// @namespace    https://github.com/kaotik4266
// @version      0.1
// @description  A very basic user script to inline images in Twitch chat.
// @author       kaotik4266
// @include      /^https?:\/\/(www\.)?twitch\.tv\/.*$/
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    const imageSuffixes = ["gif", "jpg", "png", "jpeg"];
    function isImageLink(link) {
        const tokens = link.href.split(".");
        const extension = tokens[tokens.length - 1].split("?")[0].split("#")[0];
        return imageSuffixes.includes(extension);
    }
    function alreadyHasImageChild(link) {
        return link.childNodes[0].tagName === "IMG";
    }
    function inlineTheImage(link) {
        link.innerHTML = "<img src=\"" + link.href + "\" width=300 />";
    }
    function run() {
        Array.from(document.querySelectorAll(".chat-line__message--link"))
            .filter(link => isImageLink(link))
            .filter(link => !alreadyHasImageChild(link))
            .forEach(link => inlineTheImage(link));
        setTimeout(run, 100);
    }
    run();
})();