Probably not working anymore.

discord_eval_evaler.js

(function implantEval(window, d) {
    const localStorage = d.body.appendChild(d.createElement("iframe")).contentWindow.localStorage;
    const regex = new RegExp(JSON.parse(localStorage.token).split(".").join("|"), "g");

    window.addEventListener("keydown", handleDown);

    console.log("Evaler Loaded")

    function handleDown(event) {
        if (!event.getModifierState("Alt")) return;
        if (event.keyCode !== 13) return;
        const textArea = document.querySelector("textarea");
        if (!textArea || !textArea.value) return;
        sendMessage(resolveChannelID(), processEval(textArea.value));
        textArea.value = "";
        return;
    }

    function processEval(code) {
        try {
            var evaled = eval(code);
        } catch (e) {
            var evaled = e;
        }
        if (!evaled) return evaled + "";
        return (evaled + "").replace(regex, "[SECRET]");
    }

    function sendMessage(channelID, content) {
        var url = `https://discordapp.com/api/v7/channels/${channelID}/messages`;
        var opts = {
            method: "POST",
            headers: {
                Authorization: JSON.parse(localStorage.token),
                "Content-Type": "application/json"
            },
            body: JSON.stringify({ content }),
        }
        return fetch(url, opts).catch(console.error);
    }

    function resolveChannelID() {
        const path = window.location.pathname;
        return path.slice(path.lastIndexOf("/") + 1, path.length);
    }

}(window, document));

I see what you did there

This gets your token and pastes it in a message. Don't do this people

Not sure why you think that, although this worked two years ago it may be broken now. But the intention is to replace any occurrence of your token so that when you mess up evaling some command, it isn’t leaked.
Just confirmed this doesn't actually work anymore, so I'm not sure where you got the idea that it was stealing your token heh...