Implement puppeteer's Page.addScript

lib/Page.js

@@ -62,6 +62,25 @@ class Page extends EventEmitter {
         client.on('Runtime.exceptionThrown', exception => this._handleException(exception.exceptionDetails));
     }
 
+    /**
+     * @param {string} url
+     * @return {!Promise}
+     */
+    async addScript(url) {
+        return this.evaluateAsync(addScriptTag, url);
+
+        /**
+         * @param {string} url
+         */
+        function addScriptTag(url) {
+            var script = document.createElement('script');
+            script.src = url;
+            var promise = new Promise(x => script.onload = x);
+            document.head.appendChild(script);
+            return promise;
+        }
+    }
+
     /**
      * @param {string} name
      * @param {function(?)} callback

phantomjs/WebPage.js

@@ -84,15 +84,7 @@ class WebPage {
      * @param {function()} callback
      */
     includeJs(url, callback) {
-        this._page.evaluateAsync(include, url).then(callback);
-
-        function include(url) {
-            var script = document.createElement('script');
-            script.src = url;
-            var promise = new Promise(x => script.onload = x);
-            document.head.appendChild(script);
-            return promise;
-        }
+        this._page.addScript(url).then(callback);
     }
 
     /**