如何在 Typescript 中使用 Promise.all()
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How to use Promise.all() with Typescript
提问by Greg Gum
Here is what I want to do:
这是我想要做的：
Promise.all([aurelia.start(), entityManagerProvider.initialize()])
.then((results:Array<any>) => {
let aurelia: any = results[0];
aurelia.setRoot();
});
aurelia.start()returns an Aurelia type, while initialize()returns void.
aurelia.start()返回一个 Aurelia 类型，而initialize()返回 void。
The compiler gives an error message that the type cannot be inferred from the usage.
编译器给出了一个错误消息，表明无法从用法推断出类型。
What I am trying to achieve is to get them to run at the same time, as they are both very long processes, then run Aurelia.setRoot();
我想要实现的是让它们同时运行，因为它们都是很长的进程，然后运行 Aurelia.setRoot();
回答by basarat
This is a weakness in the TypeScript and its Promise.allsignature. Its generally best to have arrays with consistent types. You can do the following manually though:
这是 TypeScript 及其Promise.all签名的弱点。通常最好拥有类型一致的数组。不过，您可以手动执行以下操作：
let foo : [Promise<Aurelia>,Promise<void>] = [aurelia.start(), entityManagerProvider.initialize()];
Promise.all(foo).then((results:any[]) => {
let aurelia: any = results[0];
aurelia.setRoot();
});
回答by Andrew Kirkegaard
Since Promise::allis a generic function, you can declare the return types of each promise like this:
由于Promise::all是一个泛型函数，你可以像这样声明每个 promise 的返回类型：
Promise.all<Aurelia, void>([
aurelia.start(),
entityManagerProvider.initialize()
])
.then(([aurelia]) => aurelia.setRoot());
回答by joonas.fi
At least from TypeScript 2.7.1onwards, the compiler seems to resolve the types without help, with a syntax like this:
至少从 TypeScript2.7.1开始，编译器似乎在没有帮助的情况下解析类型，语法如下：
Promise.all([fooPromise, barPromise]).then(([foo, bar]) => {
// compiler correctly warns if someField not found from foo's type
console.log(foo.someField);
});
Hat tip: @JamieBirch (from comment to @AndrewKirkegaard's answer)
帽子提示：@JamieBirch（从评论到@AndrewKirkegaard 的回答）
回答by John Weisz
If you'd like to keep type-safety, it's possible to extend the native type-definitionof the Promiseobject (of type PromiseConstructor) with additional overload signatures for when Promise.allis called with a finite number of not-necessarily inter-assignable values:
如果您想保持类型安全，可以使用额外的重载签名扩展Promise对象（ type PromiseConstructor）的本机类型定义，用于 whenPromise.all使用有限数量的不必要的可相互分配的值调用：
interface PromiseConstructor
{
all<T1, T2>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>]): Promise<[T1, T2]>;
all<T1, T2, T3>(values: [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>, T3 | PromiseLike<T3>]): Promise<[T1, T2, T3]>;
...
}
Add as many overloads as you need. This approach provides full type-safety for all elements in the valueargument of the onfulfilledcallback:
根据需要添加尽可能多的重载。这种方法为回调value参数中的所有元素提供了完整的类型安全onfulfilled：
Promise.all([1, "string", true]).then(value =>
{
let a: number = value[0]; // OK
let b: number = value[1]; // Type 'string' is not assignable to type 'number'.
...
});
回答by Paul T. Rawkeen
I somehow landed here when I was looking for return type of Promise.all()since straightforward [Promise<any>, Promise<any>]is obviously not working.
当我寻找返回类型时，我不知何故来到这里，Promise.all()因为直接[Promise<any>, Promise<any>]显然是行不通的。
Eventually it turned out to be simplier than it seems:
最终结果证明它比看起来更简单：
const severalMongoDbOperations: Promise<[DeleteWriteOpResultObject, UpdateWriteOpResult]> =
() => Promise.all([
mongo.deleteOne({ ... }),
mongo.updateOne({ ... })
]);
Later it can be used with .then()or:
稍后它可以与.then()or一起使用：
try {
const ops: [DeleteWriteOpResultObject, UpdateWriteOpResult] = await severalMongoDbOperations();
} catch (e) {
// Process rejection
}
