问如何使用raspberry pi node js获取加载时GPIO引脚的状态？

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var Gpio = require('onoff').Gpio; //include onoff to interact with the GPIO
var pushButton = new Gpio(18, 'in', 'both'); //use GPIO pin 18 as input, and 'both' button presses, and releases should be handled


io.sockets.on('connection', function (socket) {// WebSocket Connection
console.log("gpio status pin : ", pushButton);
  var lightvalue = 0;
  pushButton.watch(function (err, value) { //Watch for hardware interrupts on pushButton
if (err) { //if an error
  console.error('There was an error', err); //output error message to console
  return;
}
lightvalue = value;
socket.emit('light', lightvalue); //send button status to client
  });
socket.on('light', function(data){
console.log("data: ", data);
  });

});