[js] Minor tweaks for type checking

Author: jleyba

javascript/node/selenium-webdriver/lib/events.js

@@ -28,11 +28,9 @@ class Listener {
    * @param {boolean} oneshot Whether this listener should only be used once.
    */
   constructor(fn, scope, oneshot) {
-    Object.defineProperties(this, {
-      fn: {value: fn},
-      scope: {value: scope},
-      oneshot: {value: oneshot}
-    });
+    this.fn = fn;
+    this.scope = scope;
+    this.oneshot = oneshot;
   }
 }
 

javascript/node/selenium-webdriver/safari.js

@@ -363,9 +363,9 @@ class CommandExecutor {
     this.server_ = new Server();
 
     this.safari_ = this.server_.start().then(function(address) {
-      var tasks = cleanSession(
+      var tasks = /** @type {!Array<!IThenable>} */(cleanSession(
           /** @type {!Object} */(
-                command.getParameters()['desiredCapabilities']));
+                command.getParameters()['desiredCapabilities'])));
       tasks.push(
         findSafariExecutable(),
         createConnectFile(