等待并且不执行功能，直到指示灯设置为绿色 [英] Wait and don't execute a function until a light is set to green

问题描述

我了解我们可以使用.then来确保异步调用的顺序:

I understand that we could use .then to make sure the order of asynchronous calls:

return doTask1()
    .then(function () {
        return doTask2()
    })

但是有时有时会很方便，并且可以说:在灯光设置为GREEN之前，请等待并不要执行task2 ；指示灯是最初设置为RED的变量，可以通过task1或其他功能设置为GREEN.

But sometimes it will be convenient to have a light and to be able to say: wait and don't execute task2 until a light is set to GREEN; the light is a variable initially set to RED, and can be set to GREEN by task1 or other functions.

有人知道是否有可能做到这一点?

Does anyone know if it is possible to accomplish this?

我认为能够表达这一点特别有用，当我们需要结束多个任务以设置浅绿色时，而我们不知道/不注意顺序这些任务. .then不能轻易做到这一点，因为我们不知道这些任务的顺序.

Edit 1: I think being able to express this is particularly useful when we need several tasks to be ended to set the light green, and we don't know/mind the order of these tasks. .then cannot do this easily, because we don't know the order of these tasks.

关于my light，我问了一个更具体的问题.一句话，就是我们正在等待的另一个应用程序B通过postMessage发送的消息.目前，我已经编写了下面的代码(在resolve中)，该代码或多或少地起作用(我没有尝试过仅使一个功能与它们的共同部分起作用).

Edit 2: Regarding my light, I had asked a more specific question. In one word, it is the message another application B sends by postMessage that we are waiting for. At the moment, I have written the following code (which is in a resolve), which works more or less (I have not tried if making only ONE function with their common part will work).

task1: ['codeService', '$window', '$q', function (codeService, $window, $q) {
    return codeService.task1().then(function () { // task1 sends a request to another application B by postMessage
        var deferred = $q.defer();
        $window.addEventListener("message", function (event) {
            if (event.data.req === "task1ReturnFromB") deferred.resolve(event.data)
        }, { once: true });
        return deferred.promise
    })
}],
task2: ['codeService', 'task1', '$window', '$q', function(codeService, task1, $window, $q) {
    return codeService.task2().then(function () { // task2 sends a request to Application B by postMessage
        var deferred = $q.defer();
        $window.addEventListener("message", function (event) {
            if (event.data.req === "task2ReturnFromB") deferred.resolve(event.data) 
        }, { once: true });
        return deferred.promise
    })
}]

因此，在这种特定情况下，应用程序B发送的postMessage触发事件.在更一般的情况下，我想我们可能可以通过在一个应用程序中通过 dispatchEvent 来触发事件?

So in this specific case, postMessage sent by Application B triggers the event. In a more general case, I guess we could probably trigger an event by eg, dispatchEvent, in one application?

推荐答案

您还没有告诉我们有关您的light的API的信息，所以我只能猜测它是什么样子.假设它是事件驱动的模型，则可以将其转换为Promise，然后执行以下操作:

You haven't told us anything about the API for your light so I can only guess what it's like. Presuming it's an event driven model, you can convert it to a promise, and do this:

function waitForGreenLight() {
    return new Promise(function (resolve) {
        $window.addEventListener("message", function (event) {
           if (event.data.req === "task2ReturnFromB") {
               resolve(event.data) 
           }
        }, { once: true });
    });
}

return doTask1()
    .then(waitForGreenLight)
    .then(doTask2);

如果您的灯不提供事件，则可以使用waitForGreenLight定期对其进行轮询，直到其变绿为止.使用waitForGreenLight的代码将保持不变.

If your light doesn't provide events, you could have a waitForGreenLight that periodically polls it until it's green. The code to use waitForGreenLight would remain the same.

function waitForGreenLight() {
    return new Promise(function (resolve) {
        var handle = setInterval(function () { 
            if (myLight.color === 'green') { 
                resolve();
                clearInterval(handle);
            }
        }, 100);
    });
}

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