set_wakelock是一个promise方法，因此立即返回是一个promise。更改代码以等待结果

var wakeLock = await set_wakelock();

例如：

async function set_wakelock() {
  wakeLock = await navigator.wakeLock.request('screen');
  return wakeLock;
}

var wakeLock = await set_wakelock();

// Use the wakelock here...

// Release the wakelock after you have finished using it
await wakeLock.release();
wakeLock = null;

根据@derpirscher的评论，我需要以不同的方式调用release（）。

async function set_wakelock() {
    wakeLock = await navigator.wakeLock.request('screen');
    // optional listener:
    wakeLock.addEventListener('release', () => {
         alert('Wake Lock was released');
    }); 
    return wakeLock;
}

function release_wakelock(){
    if  (! wakeLock){
        return;
    }
    try {
        wakeLock.then(wls => wls.release())
        wakeLock = null;
    }  catch (err) {
        // alert(err);
    }
}

var wakeLock = null;
wakeLock =  set_wakelock();
release_wakelock();

// note: should first check that navigator.wakeLock is supported by the browser.