Question

如何修复此错误：

socket.emit('temperature',{number: data.toString().substring(69)/1000} 
                                    ^
TypeError: Cannot call method 'toString' of undefined

at /home/pi/app/mano3/app.js:28:49
at fs.js:207:20
at Object.oncomplete (fs.js:107:15)

var Gpio = require('onoff').Gpio;
var sqlite3 = require('sqlite3');
var sys = require('sys');
var gpio = require("gpio");
led = new Gpio(17, 'out');
var http = require('http');
var fs = require('fs');
var count = 0;
var db = new sqlite3.Database('./db.db');

var server = http.createServer(function(req,res){
    fs.readFile('./index.html', function(error, data){
       res.writeHead(200,{'Content-Type':'text/html'});
       res.end(data, 'utf-8');
    });
}).listen(3000);


console.log('Server is running');

var io = require('socket.io').listen(server);

io.sockets.on('connection', function(socket){
    console.log('User connected');
    setInterval(function(){
    fs.readFile('/sys/bus/w1/devices/28-00000494bf1a/w1_slave', function(error, data){
        console.log(data.toString().substring(69)/1000);
        socket.emit('temperature',{number: data.toString().substring(69)/1000});
    });
    }, 1000);
});

Answer 1

data对象没有返回值，所以我猜你在

中有错误

fs.readFile('/sys/bus/w1/devices/28-00000494bf1a/w1_slave', function(error, data){
    console.log(data.toString().substring(69)/1000);
    socket.emit('temperature',{number: data.toString().substring(69)/1000});
});

在访问数据之前先检查错误

fs.readFile('/sys/bus/w1/devices/28-00000494bf1a/w1_slave', function(error, data){
    if( error ) {
       // so something with the error
       return;
    }
    console.log(data.toString().substring(69)/1000);
    socket.emit('temperature',{number: data.toString().substring(69)/1000});
});

TypeError：无法调用未定义的方法'toString'

1 个答案: