起因：

用 element-ui 时，本人是没有安装其它环境，而是直接用链接引入，这个带来的问题是，每次打开网页都很慢，于是想本地化，但是发现只是下载两个引入的 js 和 css 是不够的，很多功能会无法使用，打开 DevTools 发现是还有别的资源本地没有。

再次前往官网，找到下载页面，结果发现并没有给直接的下载链接。。没办法了，自己写个脚本来下载。最后成功离线化。

下载后在 html 中引入：

<!--<link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css">-->
<link rel="stylesheet" href="element-ui/lib/theme-chalk/index.css" rel="external nofollow" >

<!--<script src="https://unpkg.com/element-ui/lib/index.js"></script>-->
<script src="element-ui/lib/index.js"></script>

下载脚本：

临时起意做的，代码里面可能会有些瑕疵，但是不影响使用，本人已经成功下载并使用。
路径可以自己更改，注意不要从 Windows 资源管理器复制，Linux 系统当我没说。

package com.ycr;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;

public class Main {
 static String fileP = "C:\\Users\\YCR\\Desktop\\element-ui\\"; // 不要从资源管理器复制，有的字符会有问题，导致无法创建文件
 static String urlP = "https://unpkg.com/browse/element-ui@2.12.0/";
 static String urlF = "https://unpkg.com/element-ui@2.12.0/";
 public static void main(String[] args){
 try {
  GetPage("");
 } catch (Exception e) {
  e.printStackTrace();
 }
 }
 static void GetPage(String after) throws Exception {
 System.out.println(urlP + after);
 new File(fileP + after).mkdir();
 HttpURLConnection http = (HttpURLConnection) (new URL(urlP + after)).openConnection();
 http.setRequestMethod("GET");
 http.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3562.0 Safari/537.36");
 http.connect();
 if(http.getResponseCode() == 200) {
      InputStream inputStream = http.getInputStream();
      byte [] buffer = new byte[1024];
      ArrayList<byte []> byteList = new ArrayList<>();
      ArrayList<Integer> byteLength = new ArrayList<>();
      int length;
      int totalLength = 0;
      while( (length = inputStream.read(buffer)) != -1 ) {
       byteList.add(buffer);
       byteLength.add(length);
       totalLength += length;
       buffer = new byte[1024];
      }
      http.disconnect();
      byte [] all;
      all = new byte[totalLength];
      totalLength = 0;
      while(byteList.size() != 0) {
       System.arraycopy(byteList.get(0), 0, all, totalLength, byteLength.get(0));
       totalLength += byteLength.get(0);
       byteList.remove(0);
       byteLength.remove(0);
      }
      String content = new String(all, StandardCharsets.UTF_8);
      all = null;
      content = content.split("tbody")[1];
      String [] us = content.split("href=\"");
      for(int i = 1; i < us.length; i ++) {
       String href = us[i].split("\"", 2)[0];
       if(href.equals("../")) {
      continue;
     }
       if(href.charAt(href.length() - 1) == '/') {
       GetPage(after + href);
       } else {
       GetFile(after + href);
       }
      }
    } else {
  GetPage(after);
 }
 }
 static void GetFile(String url) throws Exception{
 System.out.println(url);
 HttpURLConnection http;
 http = (HttpURLConnection) (new URL(urlF + url)).openConnection();
 http.setRequestMethod("GET");
 http.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3562.0 Safari/537.36");
 http.connect();
 if(http.getResponseCode() == 200) {
      InputStream inputStream = http.getInputStream();
      byte [] buffer = new byte[1024];
      ArrayList<byte []> byteList = new ArrayList<>();
      ArrayList<Integer> byteLength = new ArrayList<>();
      int length;
      int totalLength = 0;
      while( (length = inputStream.read(buffer)) != -1 ) {
       byteList.add(buffer);
       byteLength.add(length);
       totalLength += length;
       buffer = new byte[1024];
      }
      http.disconnect();
      byte [] all;
      all = new byte[totalLength];
      totalLength = 0;
      while(byteList.size() != 0) {
       System.arraycopy(byteList.get(0), 0, all, totalLength, byteLength.get(0));
       totalLength += byteLength.get(0);
       byteList.remove(0);
       byteLength.remove(0);
      }
      File f = new File(fileP + url.replaceAll("/", "\\\\"));
      f.createNewFile();
      FileOutputStream fos = new FileOutputStream(f, false);
      fos.write(all);
      fos.flush();
      fos.close();
 } else {
  GetFile(url);
 }
 }
}