javascript - Promises 中的异步函数

Question

这是我的情况:

fetchData(foo).then(result => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve(result + bar);
        }, 0)
    });
}).then(result => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve( result + woo);
        }, 0)
    });
}).then(result => {
    setTimeout(() => {
        doSomething(result);
    }, 0)
});

其中每个 setTimeout 都是使用回调模式的不同异步操作。

将每个函数都包装在一个 promise 中真的很痛苦，我觉得代码应该看起来更像这样:

fetchData(foo).then(result => {
    setTimeout(() => {
        return result + bar;
    }, 0)
}).then(result => {
    setTimeout(() => {
        return result + woo;
    }, 0)
}).then(result => {
    setTimeout(() => {
        doSomething(result);
    }, 0)
});

显然这行不通。

我是否正确使用了 Promises？我真的必须将所有现有的异步函数包装在 promises 中吗？

编辑:

实际上，我意识到我的例子并不能完全代表我的情况，我没有明确表示我的例子中的 setTimeout 是为了代表异步操作。这种情况更能代表我的情况:

fetchData(foo).then(result => {
    return new Promise((resolve, reject) => {
        asyncOperation(result, operationResult => {
            resolve(operationResult);
        }, 0)
    });
}).then(result => {
    return new Promise((resolve, reject) => {
        otherAsyncOperation(result, otherAsyncResult => {
            resolve( otherAsyncResult);
        }, 0)
    });
}).then(result => {
        doSomething(result);
});

Answer 1

Am I using Promises right? Do I really have to wrap all existing async function in promises?

是的。是的。

I feel like the code should look more like this

不，不应该。它应该看起来像这样:

function promiseOperation(result) {
    return new Promise((resolve, reject) => {
        asyncOperation(result, resolve, 0)
    });
}
function otherPromiseOperation(result) {
    return new Promise((resolve, reject) => {
        otherAsyncOperation(result, resolve, 0)
    });
}

fetchData(foo).then(promiseOperation).then(otherPromiseOperation).then(doSomething);

It is really painfull to wrap each function inside a promise

嗯，不要每次都重复写出来。您可以将此包装抽象为一个函数!

function promisify(fn) {
    return value => new Promise(resolve => {
        fn(value, resolve, 0)
    });
}
const promiseOperation = promisify(asyncOperation);
const otherPromiseOperation = promisify(otherAsyncOperation);
fetchData(foo).then(promiseOperation).then(otherPromiseOperation).then(doSomething);

请注意，大多数 promise 库都包含这样的 promisification 函数，因此您的整个代码减少到这三行。