在解决原始承诺之前等待嵌套的 JS 承诺完成 [英] Wait for nested JS promise to finish before resolving original promise
问题描述
我是 Promises 的新手，我在解决原始承诺之前等待嵌套承诺完成所有执行的概念有点麻烦.
I am new to Promises and I'm having a little trouble with the concept of waiting for a nested promise to finish all executions before resolving the original promise.
原始代码
function getSomething(text) {
return new Promise(function (resolve, reject) {
getElse(text).then(function (items) {
if (items.length !== 0) {
/* Stuff here */
getElseElse(box).then(function (moreItems) {
/* Stuff here */
return array;
}.then(function (array) {
var promise = new Promise(function (resolve, reject) {
/* anotherFunction() is asynchronous */
result = anotherFunction(array); <-- Spot 1
});
promise.then(function () { });
});
return resolve(result); <--- Spot 2
}
else {
return resolve(null);
}
});
});
};
更新代码 - 更好，但仍然没有像我想要的那样完全工作.
Updated Code - better but still not fully working like I want.
function getSomething(text) {
return getElse(text).then(function (items) {
if (items.length !== 0) {
/* Stuff here */
return getElseElse(box).then(function (moreItems) {
/* Stuff here */
return array;
}).then(anotherFunction);
} else {
return null;
}
});
}
然后，在单个视图页面内，我有这个:
Then, inside of the individual View page, I have this:
getSomething(text).then(function (result) {
/* Do something here using result */
/* But result is undefined and I think still pending */
});
我已经使用 Thomas 的帮助优化了原始函数，但在制定 result 之前，视图中的原始调用似乎仍在继续.
I have optimized the original function using Thomas's help but the original call inside the view still seems to be continuing before result is formulated.
我希望 getSomething() 在执行视图内的 .then 内的代码之前完成并返回 result.到目前为止，这还没有完成.
I want getSomething() to full complete and return result before I execute the code inside of the .then that is inside the view. So far, that is not being accomplished.
我发现了一些帖子，它们指出了我认为 Promise.all 的正确方向，但我似乎无法获得这些信息，所以我希望有人可以帮助解释我的具体情况.
I have found a couple posts that have pointed me in what I think is the correct direction of Promise.all but I can't really seem to get anywhere with that information so I was hoping someone could help explain it for my specific situation.
有帮助的帖子是:
解决方案
托马斯在标记答案中解决了原始问题.经过进一步检查，最终问题在 anotherFunction() 内部得到解决.
原来:
function anotherFunction(array) {
return new Promise(function (resolve, reject) {
return anotherGet(parcels).then(function (list) {
/* Do stuff here without a return */
});
});
}
固定版本:
function anotherFunction(array) {
return anotherGet(parcels).then(function (list) {
/* Do stuff here */
return list;
});
}
推荐答案
首先，避免 Promise/Deferred 反模式.您很少需要创建自己的 Promise，通常您有一些返回 Promise 的函数；用那个.
First, avoid the Promise/Deferred antipattern. Rarely you need to create your own promises, usually you have some function that returns a Promise; use that.
其次，为了让外层 Promise 等待一个需要的 PROmise，你需要将嵌套的 Promise 返回给外层 Promise.
在 then() 中返回一个 Promise 将使生成的 Promise 解析为您在内部重新调整的 Promise 的值.
Second, for the outer Promise to wait for a nesed PRomise, you need to return that nested Promise to the outer Promise.
Returning a Promise inside of then() will make the resulting Promise to resolve to the value of the Promise you retuned inside.
最后，类似于 .then(value => value) 或 .then(value => Promise.resolve(someFunction(value))) 是无意义.您对 anotherFunction 的包装基本上只是通过了参数并返回了结果.
And last, something like .then(value => value) or .then(value => Promise.resolve(someFunction(value)))is pointless. Your wrapper around anotherFunction basically just passed through the argument and returned the result.
因此，您的伪代码应如下所示:
So, your Pseudocode should look something like this:
function getSomething(text) {
return getElse(text).then(function (items) {
if (items.length !== 0) {
/* Stuff here */
return getElseElse(box).then(function (moreItems) {
/* Stuff here */
return array;
}).then(anotherFunction);
} else {
return null;
}
});
}
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