Script to switch recommended works on pixiv to show only R-18 works

allows you to display only R-18 works in the recommended works at the bottom of the artwork page.
目前為 2021-03-08 提交的版本，檢視最新版本。
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/*jshint esversion: 6 */

// ==UserScript==
// @name        Script to switch recommended works on pixiv to show only R-18 works
// @name:ja           pixivの関連作品をR-18オンリーと切り替えるスクリプト
// @name:zh-CN     将pixiv上的推荐作品切换为只显示R-18的Script
// @description allows you to display only R-18 works in the recommended works at the bottom of the artwork page.
// @description:ja pixivの作品画面の下部に表示される関連作品を、R-18作品に絞って表示することができます。
// @description:zh-cn 它可以让您在作品页面底部的推荐作品中只显示R-18作品。
// @version        0.5.1
// @author         Qappendix
// @license        GPL v3; https://www.gnu.org/copyleft/gpl.html
// @match          *://www.pixiv.net/*
// @grant          GM_setValue
// @grant          GM_getValue
// @namespace https://greasyfork.org/users/724570
// ==/UserScript==

(function() {
//変数初期化

let recommendSection = null;
let href = location.href;
let artworkUrl = /^(http|https):\/\/(www)?\.pixiv\.net\/artworks\/.*/;

let isEnabled = GM_getValue('isEnabled', true);

let allIllustsSet = new Set();
let sensitiveIllustsSet = new Set();

///ボタン要素追加

let switchButton = document.createElement('button');
let switchButtonStyle = 'position: fixed; bottom: 10px; right: 10px; padding: 6px 40px;';
let ONText = 'R-18 only: ON';
let OFFText = 'R-18 only: OFF';

switch(isEnabled){
      case true:
         switchButton.innerHTML = ONText;
         break;
      case false:
         switchButton.innerHTML = OFFText;
         break;
}

switchButton.id = 'switch_button';
switchButton.setAttribute('Style', switchButtonStyle)

document.body.appendChild(switchButton);

//ボタンクリック時イベント定義

switchButton.addEventListener('click', function(){
   switch(isEnabled){
      case true:
         isEnabled = false;
         switchButton.innerHTML = OFFText;
         if(artworkUrl.test(href)){ location.reload(); }
         break;
      case false:
         isEnabled = true;
         switchButton.innerHTML = ONText;
         enableObservation();
         break;
   }
   GM_setValue('isEnabled',isEnabled);
});

///MutationObserver定義

let documentObserver = new MutationObserver( function(){
   if(href !== location.href){
      href = location.href;
      recommendSection = null;
      recommendObserver.disconnect();
      allIllustsSet.clear();
      sensitiveIllustsSet.clear();
      return;
   }

   if(artworkUrl.test(href)){
      enableObservation();
   }
})

let recommendObserver = new MutationObserver( function(){
   deleteNotSensitiveIllust(recommendSection);
})

//文書全体の変更を監視

documentObserver.observe(document, {attributes: true, subtree: true});

///関数定義

function enableObservation(){
   if(!isEnabled || !artworkUrl.test(href)){ return; }

   recommendSection = updateRecommendSection(recommendSection);
   if(recommendSection){
      recommendObserver.observe(recommendSection, {attributes: true, subtree: true});
   }
}

function updateRecommendSection(recom){
   if(recom){
      deleteNotSensitiveIllust(recom);
      return recom;
   }else if(!recom){
      for(let section of document.body.getElementsByTagName("section")){
         for(let div of section.getElementsByTagName("div")){
            if(div.textContent == "関連作品" || div.textContent == "おすすめ作品"){
               recom = section;
               deleteNotSensitiveIllust(recom);
               return recom;
            }
         }
      }
   }
}

function deleteNotSensitiveIllust(recom){
   if(!recom){ return; }

   Array.prototype.forEach.call(recom.getElementsByTagName("li"), function(li){
      allIllustsSet.add(li);
      if(li.textContent.indexOf("R-18")!=-1){
            sensitiveIllustsSet.add(li);
      }
   })
   if(sensitiveIllustsSet.size!=0){
       for(let work of allIllustsSet){
           if(!sensitiveIllustsSet.has(work)){work.remove();}
       }
   }
}

})()