ReferenceError: path is not defined at Object.handle
<p>js file,</p>

<pre><code>app.get('/',function(req,res){
    res.sendfile(_dirname + '/index.html');
});
</code></pre>

<p>node.js can start ,but I got this error,</p>

<blockquote>
  <p>ReferenceError: path is not defined at Object.handle
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\app.js:12:15)
  at next_layer
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\route.js:103:13)
  at Route.dispatch
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\route.js:107:5)
  at
  E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\index.js:195:24
  at Function.proto.process_params
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\index.js:251:12)
  at next
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\index.js:189:19)
  at Layer.expressInit [as handle]
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\middleware\init.js:23:5)
  at trim_prefix
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\index.js:226:17)
  at
  E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\index.js:198:9
  at Function.proto.process_params
  (E:\javaEEstudy\node.js\node.js入门经典\socket\socket.io_express\node_modules\express\lib\router\index.js:251:12)</p>
</blockquote>

<p>the index.html and app.js is on the same file ,express version is 4.x</p>