没有复制nodejs数组?

我使用nodejs制作了一个状态机,使用串行端口,我需要接收和发送一系列命令来验证通信是否正确,在我的第二个状态下,我接收到31字节的数据,需要在第四个状态下重新发送,因为我只需复制接收到的数组来发送它。稍后,但在我的第四个状态控制台上,日志没有显示任何内容,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;
    }
}