Add English toggle

book.toml

@@ -5,5 +5,6 @@ authors = ["The Rust Project Developers"]
 src = "src"
 
 [output.html]
+additional-js = ["language.js"]
 # English git-repository-url = "https://github.com/rust-lang/rust/tree/master/src/doc/rustdoc"
 git-repository-url = "https://github.com/rust-lang-cn/rustdoc-cn"

language.js

@@ -0,0 +1,54 @@
+(function () {
+  var url = window.location.href;
+  var host = window.location.host;
+  var home_url = window.location.protocol + '//' + window.location.host;
+
+  var search = {
+    en: "/en/",
+    zh_CN: "/zh-CN/"
+  }
+
+  var replaceWith = {
+    en: "/zh-CN/",
+    zh_CN: "/en/"
+  }
+
+  var link = "";
+  var word = "";
+  var home = "Home";
+  var lang = "zh-CN";
+  var changeLang = "切换到英语";
+
+  if (url.indexOf(search.en) != -1 && url.indexOf(search.en) === (url.indexOf(host) + host.length)) {
+    link = url.replace(search.en, replaceWith.en);
+    word = "简体中文";
+    lang = "en";
+    changeLang = "Switch to Chinese"
+  } else if (url.indexOf(search.zh_CN) != -1 && url.indexOf(search.zh_CN) === (url.indexOf(host) + host.length)) {
+    link = url.replace(search.zh_CN, replaceWith.zh_CN);
+    word = "English";
+	  home = "首页";
+  }
+
+  var edit_id = document.getElementById("git-edit-button");
+  if (edit_id != null && edit_id.parentNode != null) {
+    edit_id.parentNode.target = "_blank";
+    if (lang != "en") {
+      edit_id.parentNode.title = "报告错误或改进本页翻译";
+    }
+  }
+
+  var home_node = '';
+  if (window.location.protocol == 'http:' || window.location.protocol == 'https:') {
+    home_node = '<a href="' + home_url + '" title="' + home + '" aria-label="' + home + '"><i id="go-back-homepage" class="fa fa-home"></i></a>';
+  }
+  var lang_node = '';
+  if (link != '') {
+    lang_node = '<a href="' + link + '" title="' + changeLang + '" aria-label="' + changeLang + '"><i id="change-language-button" class="fa fa-language"> ' + word + '</i></a>';
+  }
+  var insertNode = document.getElementsByClassName('right-buttons');
+  if (insertNode.length > 0) {
+    var html = insertNode[0].innerHTML;
+    insertNode[0].innerHTML = home_node + html + lang_node;
+  }
+})()