1.请确保myId不为空，因为当您第一次调用navigator.mediaDevices.enumerateDevices()时，它可能返回空字符串。
1.对于我const constraints = {audio: {deviceId: {exact: myId}}};返回错误，因为exact。对于我工作const constraints = {audio: {deviceId: myId}};

1. const constraints = {audio: {deviceId: {exact: myId}};结尾缺少一个'}'。
   1.如果您设置新设备，您必须从新流中获取新曲目并添加到旧流中。
   这是一个工作代码，它根据您单击按钮来改变麦克风
   script.js

let mediaStream;
let mic1Id, mic2Id;
navigator.mediaDevices.enumerateDevices().then((res) => {
    mic1Id = res[2].deviceId;
    mic2Id = res[3].deviceId;
    const constraints = {
        audio: {
            deviceId: { exact: mic1Id },
        },
    };
    navigator.mediaDevices.getUserMedia(constraints).then((stream) => {
        mediaStream = stream;

        var audio = document.querySelector("audio");
        stream.getAudioTracks()[0].enabled = true;

        audio.srcObject = stream;
    });
});

function getAudioTrack(deviceId) {
    const constraints = {
        audio: {
            deviceId: {
                exact: deviceId,
            },
        },
    };
    return navigator.mediaDevices.getUserMedia(constraints).then((stream) => {
        return stream.getAudioTracks();
    });
}

function replaceAudioTrack(stream, newAudioTrack) {
    let audioTrack = stream.getAudioTracks()[0];
    stream.removeTrack(audioTrack);
    stream.addTrack(newAudioTrack);
}

let btn1 = document.querySelector("button:nth-of-type(1)");
let btn2 = document.querySelector("button:nth-of-type(2)");

btn1.onclick = () => {
    getAudioTrack(mic1Id).then((res) => replaceAudioTrack(mediaStream, res[0]));
};
btn2.onclick = () => {
    getAudioTrack(mic2Id).then((res) => replaceAudioTrack(mediaStream, res[0]));
};

index.html

<audio autoplay></audio>
    <button>Mic 1</button>
    <button>Mic 2</button>