在Array#map()中异步/等待 [英] Async/Await inside Array#map()

问题描述

此代码出现编译时错误:

const someFunction = async (myArray) => {
    return myArray.map(myValue => {
        return {
            id: "my_id",
            myValue: await service.getByValue(myValue);
        }
    });
};

错误消息是:

await是保留字

为什么我不能像这样使用它?

我也尝试了另一种方法，但是它给了我同样的错误:

 const someFunction = async (myArray) => {
    return myArray.map(myValue => {
        const myNewValue = await service.getByValue(myValue);
        return {
            id: "my_id",
            myValue: myNewValue 
        }
    });
};

解决方案

您不能像您想象的那样执行此操作，因为如果await不是直接在async函数内部，则不能使用. >

在这里要做的明智的事情是使传递给map的函数异步.这意味着map将返回一个promise数组.然后，当所有的诺言都返回时，我们可以使用Promise.all获得结果.当Promise.all本身返回一个promise时，外部函数不必是async.

const someFunction = (myArray) => {
    const promises = myArray.map(async (myValue) => {
        return {
            id: "my_id",
            myValue: await service.getByValue(myValue)
        }
    });
    return Promise.all(promises);
}

I'm getting compile time error with this code:

const someFunction = async (myArray) => {
    return myArray.map(myValue => {
        return {
            id: "my_id",
            myValue: await service.getByValue(myValue);
        }
    });
};

Error message is:

await is a reserved word

Why can't I use it like this?

I also tried another way, but it gives me same error:

 const someFunction = async (myArray) => {
    return myArray.map(myValue => {
        const myNewValue = await service.getByValue(myValue);
        return {
            id: "my_id",
            myValue: myNewValue 
        }
    });
};

解决方案

You can't do this as you imagine, because you can't use await if it is not directly inside an async function.

The sensible thing to do here would be to make the function passed to map asynchronous. This means that map would return an array of promises. We can then use Promise.all to get the result when all the promises return. As Promise.all itself returns a promise, the outer function does not need to be async.

const someFunction = (myArray) => {
    const promises = myArray.map(async (myValue) => {
        return {
            id: "my_id",
            myValue: await service.getByValue(myValue)
        }
    });
    return Promise.all(promises);
}

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