Question

我正在使用NodeJS制作状态机，并使用串行端口接收和发送一系列命令以验证通信是否正确，在第二个状态下，我接收了31个字节的数据，并需要在我的设备上重新发送它们第四种状态，为此，我只是复制接收到的数组以稍后发送，但是在我的第四种状态console.log上什么都没有显示，会发生什么？

这是我的代码：

const SerialPort = require('serialport');
const ByteLength = SerialPort.parsers.ByteLength;
const port = new SerialPort("COM6");
const parser = new ByteLength({length: 1});
port.pipe(parser);

var state = 0;
var cache = [];
var history;

parser.on('data', function (data) {
    cache.push(data[0]);
    flowcontrol();
});

function porterr() {
    console.log('error');
    process.exit(1);
}

function flowcontrol() {

    switch (state) {
        case 0:
            // ---------------------------------------------
            //  State 0 -> Recives ENQ, Sends ACK
            // ---------------------------------------------
            // Receives 1 byte
            if (cache.length !== 1) {
                return;
            }

            // Verify answer received
            if (cache[0] !== 5) {
                // Wrong answer received
                porterr();
            }

            console.log('state ' + state);
            // Sends Answer, clears cache, and waits for next state
            port.write(Buffer.from([6]));
            state++;
            cache.length = 0;
            break;

        case 1:
            // ---------------------------------------------
            //  State 1 -> Recives DATA, Sends ACK
            // ---------------------------------------------
            // Receives 31 bytes
            if (cache.length !== 31) {
                return;
            }

            console.log('state ' + state);
            history = cache; // <--- data is saved for later use

            // Sends Answer, clears cache, and waits for next state
            port.write(Buffer.from([6]));
            state++;
            cache.length = 0;
            break;

        case 2:
            // ---------------------------------------------
            //  State 1 -> Recives EOT, Sends ENQ
            // ---------------------------------------------
            // Receives 1 byte
            if (cache.length !== 1) {
                return;
            }

            // Verify answer received
            if (cache[0] !== 4) {
                // Wrong answer received
                porterr();
            }

            console.log('state ' + state);
            // Sends Answer, clears cache, and waits for next state
            port.write(Buffer.from([5]));
            state++;
            cache.length = 0;
            break;

        case 3:
            // ---------------------------------------------
            //  State 3 -> Recives ACK, Sends DATA
            // ---------------------------------------------
            // Receives 1 byte
            if (cache.length !== 1) {
                return;
            }

            // Verify answer received
            if (cache[0] !== 6) {
                // Wrong answer received
                porterr();
            }

            console.log('state ' + state);
            console.log[history]; // <-- Nothing is shown here!!!

            // Sends Answer, clears cache, and waits for next state
            //port.write(Buffer.from(history));
            //state++;
            //cache.length = 0;
            break;

        default:
            console.log('not yet completed');
            console.log(cache.length);
            break;
    }
}

Answer 1

您不应分配与javascript相等的对象。

为此使用Object.assign或lodash。

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign

https://lodash.com/docs/4.17.10#cloneDeep

代码中发生的事情是当您更改cache.length = 0的值时；它也改变了历史的价值。因为它是对象而不是引用类型。

nodejs数组没有被复制？

1 个答案: