Adds a watch online button on the anime page on shikimori.one

shikimori-watch-online-button.user.js

// ==UserScript==
// @name         Shikimori.one anime watch button
// @name:ru      Кнопка "смотреть онлайн" на shikimori.one
// @namespace    https://shikimori.one/
// @version      0.2
// @description  Adds a watch online button on the anime page
// @description:ru Добавляет кнопку "смотреть онлайн" на странице аниме shikimori.one
// @author       BoberMod
// @match        https://shikimori.one/animes/*
// @downloadURL  https://gist.github.com/BoberMod/08962097fe888a7c4cf83ab79e28863f/raw/shikimori-watch-online-button.user.js
// @updateURL    https://gist.github.com/BoberMod/08962097fe888a7c4cf83ab79e28863f/raw/shikimori-watch-online-button.user.js
// @grant        none
// ==/UserScript==

function add() {
    "use strict";

    let watch = document.getElementsByClassName("watch-online-placeholer")[0];
    let block = document.createElement("div");
    let watchButton = document.createElement("A");

    block.setAttribute("class", "block");
    watchButton.text = "Смотреть онлайн";
    watchButton.setAttribute("class", "b-link_button dark watch-online");
    watchButton.setAttribute('href', "https://play.shikimori.org" + window.location.pathname);

    watch.appendChild(block);
    block.appendChild(watchButton);
}

function onload(fn) {
    document.addEventListener('page:load', fn);
    document.addEventListener('turbolinks:load', fn);

    if (document.attachEvent ? document.readyState === "complete" : document.readyState !== "loading") {
        fn();
    } else {
        document.addEventListener('DOMContentLoaded', fn);
    }
}

onload(add);