javascript - 如何有条件地等待 promise 解决？

Question

我调用一个函数，

getResponse(Math.random());
doSomethingWith(someVar);


getResponse(num) {
  if(num > 0.8) someVar = "whee";
  if(num > 0.5) someVar = "whoo";
  if(num > 0) callSomeOtherFunctionWhichDoesABunchOfDatabaseQueriesThatUsePromisesAndEventuallySetssomeVar();
}

有没有一种方法可以等待 callSomeOtherFunctionWhichDoesABunchOfDatabaseQueriesThatUsePromisesAndEventuallySetssomeVar() 完成并设置 someVar ？我在想我也可以将 someVar 的赋值包装在一个 promise 中，然后使 getResponse then() 能够，但这似乎有点过多，因为我只有一个案例，我有一堆异步工作正在完成以确定 someVar。

Answer 1

Note, replaced callSomeOtherFunctionWhichDoesABunchOfDatabaseQueriesThatUsePromisesAndEventuallySetssomeVar with someFunc in code below :p

getResponse 总是需要返回一个 promise

所以

function getResponse(num) {
    return Promise.resolve()
    .then(() => {
        if (num > 0.8) {
            someVar = "whee";
            return;
        }
        if (num > 0.5) {
            someVar = "whoo";
            return;
        }
        if (num > 0) {
            return someFunc();
        }
    });
}

请注意 - 原始代码中的逻辑(几乎)总是运行那个冗长的函数，因为 Math.random() 几乎总是 > 0

剩下的代码就是

getResponse(Math.random())
.then(() => doSomethingWith(someVar));

if someFunc resolves to the value it sets someVar to, you could make the code a little nicer

var getResponse = num => Promise.resolve()
.then(() => {
    if (num > 0.8) {
        return "whee";
    }
    if (num > 0.5) {
        return "whoo";
    }
    return someFunc();
});

getResponse(Math.random())
.then(someValue => doSomethingWith(someValue));

但如果 someVar 以其他方式使用，那可能就没用了