Javascript过滤器方法返回原始数组，即使返回false

Question

我有一个过滤器方法如下:

let newArray = Alerts[symbol].filter(async (alert: IDiscordSymbolAlert, alert_index: number) => {
// If Price when set is greater than alert price, price has to move UP to trigger
if (alert.price_when_set < alert.alert_price) {
hasToGo = Change.UP;
} 
// If Price when set is greater than alert price, price has to move DOWN to trigger
else if (alert.price_when_set > alert.alert_price){
hasToGo = Change.DOWN;
}
/**If the hasToGo is UP and current price is greater than alert price, then ALERT USER [OR]
// If the hasToGo is DOWN and current price is lesser than alert price, then ALERT USER **/ 
if((hasToGo === Change.UP && (price >= alert.alert_price)) ||
(hasToGo === Change.DOWN && (price <= alert.alert_price))) {
/**
* Send Notification that alert has been hit
*/
let userToSend = await discord.users.fetch(alert.userID)
if(!userToSend) return;
//@ts-ignore
userToSend.send(`> @everyonenn${symbol} has reached your alert price - ${alert.alert_price}`);
// remove that alert
guild_modified = true;
return false;
}
return true;
});

// When logged here, it shows the entire array even though certain values have returned false.
// I know they returned false because the block in which they returned false was executed and 
//i did receive a notification which was executed in the same block.
console.log(newArray);

在这里记录(console.log)时，即使某些值返回false，它也会显示整个数组。我知道它们返回false，因为它们返回false的块被执行，并且我确实收到了在同一块中执行的通知。我知道这与async/await有关，但我不确定是什么。谁来帮我看看。

<<p>更新问题/strong>

Alerts[symbol].forEach(async (alert: IDiscordSymbolAlert, alert_index: number) => {
// If Price when set is greater than alert price, price has to move UP to trigger
if (alert.price_when_set < alert.alert_price) {
hasToGo = Change.UP;
} 
// If Price when set is greater than alert price, price has to move DOWN to trigger
else if (alert.price_when_set > alert.alert_price){
hasToGo = Change.DOWN;
}
/**If the hasToGo is UP and current price is greater than alert price, then ALERT USER [OR]
// If the hasToGo is DOWN and current price is lesser than alert price, then ALERT USER **/ 
if((hasToGo === Change.UP && (price >= alert.alert_price)) ||
(hasToGo === Change.DOWN && (price <= alert.alert_price))) {
/**
* Send Notification that alert has been hit
*/
let userToSend = await discord.users.fetch(alert.userID)
if(!userToSend) return;
//@ts-ignore
userToSend.send(`> @everyonenn${symbol} has reached your alert price - ${alert.alert_price}`);
// remove that alert
Alerts![symbol].splice(alert_index, 1);
guild_modified = true;
}
});
console.log(Alerts[symbol]);

因为过滤器不能在这种情况下使用async/await。这是我使用forEach()循环并使用splice()手动删除数组中匹配的对象。但是由于forEach本身是异步的，并且console.log在异步块之外起作用。它返回的不是新数组，而是未修改的数组。如何返回在forEach块作用域之外使用的新数组?

提前感谢!

Answer 1

不能将async函数与filter一起使用。filter返回回调函数返回真值的所有元素。async函数总是返回承诺，承诺是对象，所有非null对象都是真值。

如果你的filter检查需要async，你的整个操作是async，需要这样处理。

这是一个现成的async过滤函数，它并行地执行元素检查。同样，像所有async函数一样，它返回结果的承诺:

async function filterAsync(array, callback, thisArg = undefined) {
const flags = await Promise.all(array.map(callback, thisArg));
const result = [];
for (let n = 0; n < array.length; ++n) {
if (flags[n]) {
result.push(array[n]);
}
}
return result;
}

要使用它，你必须消费承诺:

// In an `async` function (assuming you want errors to propagate):
const newArray = await filterAsync(Alerts[symbol], element => /*...keep-or-toss logic...*/);
// ...use `newArray`...

或

// Not in an `async` function
filterAsync(Alerts[symbol], element => /*...keep-or-toss logic...*/)
.then(newArray => {
// ...use `newArray`...
})
.catch(error => {
// ...handle/report error...
});