javascript - Node.js 函数、对象和变量

Question

我刚刚开始使用 javascript，我仍在努力了解它是如何工作的。

你能解释一下为什么会这样吗

serialPort.on("open", function () {
    console.log('open');
    serialPort.on('data', function(data) {
        console.log('data received: ' + data);
        //socket.emit('test', { arduinotest: 'Arduino Connected'});
    });  
});

这不是，我收到“数据未定义错误”

serialPort.on("open", function () {
    console.log('open');
    serialPort.on('data', received(data));  
});

function received(data) {
    console.log('data received: ' + data);
    //socket.emit('test', { arduinotest: 'Arduino Connected'});
}

我不喜欢有很多嵌套函数，应该如何将函数分离出来？

这是我的全部代码

var app = require('express')()
    , server = require('http').createServer(app)
    , io = require('socket.io').listen(server)
    , SerialPort  = require('serialport').SerialPort;

//SERIAL
var portName = '/dev/ttyACM0';
var serialPort = new SerialPort(portName, {
    baudRate: 115200,
    dataBits: 8,
    stopBits: 1,
    parity: 'none',   
});

serialPort.on("open", function () {
    console.log('open');
    serialPort.on('data', function(data) {
        console.log('data received: ' + data);
        //socket.emit('test', { arduinotest: 'Arduino Connected'});
    });  
});

//SERVER
app.get('/', function (req, res){
    res.sendfile(__dirname + '/index.html');
});

io.sockets.on('connection', function (socket){
    socket.emit('test', { servertest: 'Server Connected' });
    socket.on('value', function (data){
        switch(data.key)
        {
        case "Right":
            if(data.state == "True")
            {
                serialPort.write("d180\n");
                console.log("test RT");
            }
            else if(data.state == "False")
            {
                serialPort.write("d90\n");
                console.log("test RF");
            }      
            break;
        case "Left":
            if(data.state == "True")
            {
                serialPort.write("d0\n");
                console.log("test LT");
            }
            else if(data.state == "False")
            {
                serialPort.write("d90\n");
                console.log("test LF");
            }      
            break;
        case "Up":
            if(data.state == "True")
            {
                serialPort.write("s0\n");
                console.log("test UT");
            }
            else if(data.state == "False")
            {
                serialPort.write("s90\n");
                console.log("test UF");
            }      
            break;
        case "Down":
            if(data.state == "True")
            {
                serialPort.write("s180\n");
                console.log("test DT");
            }
            else if(data.state == "False")
            {
                serialPort.write("s90\n");
                console.log("test DF");
            }      
            break;
        }
    });
});

server.listen(9081, '192.168.1.158');

我应该如何从我的串行端口代码(注释掉的行)中访问我的套接字对象？

感谢帮助我理解

乔

Answer 1

在第二个示例中，您编写了 serialPort.on('data', received(data)); 它将立即调用 received 函数，并将on 监听器的第二个参数的结果。

相反，您只想执行 serialPort.on('data', received); 传递 received 函数本身，这意味着监听器可以在准备就绪时调用它.