title: ReferenceError: path is not defined at Object.handle
body: <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>