add external-script plugin

lib/plugins/external-script.js

@@ -0,0 +1,30 @@
+this.D = this.D || {};
+(function () {
+'use strict';
+
+var scriptReg = /<script[^>]*src=["|'](.*)["|']>[^\w]*<\/script>/;
+var asyncReg = /<script[^>]*\s+async/;
+var deferReg = /<script[^>]*\s+defer/;
+
+function handleExternalScript (html) {
+  var scriptMatch = html.match(scriptReg);
+
+  if (scriptMatch && scriptMatch.length > 1) {
+    var script = document.createElement('script');
+    script.src = scriptMatch[1];
+
+    if (asyncReg.test(scriptMatch[0])) { script.setAttribute('async', ''); }
+    if (deferReg.test(scriptMatch[0])) { script.setAttribute('defer', ''); }
+
+    var target = document.querySelector('#main');
+    target.appendChild(script);
+  }
+}
+
+var install = function (hook) {
+  hook.afterEach(handleExternalScript);
+};
+
+window.$docsify.plugins = [].concat(install, window.$docsify.plugins);
+
+}());