如何简化Q承诺示例 [英] How to simplify Q promise example

问题描述

我正在开发一个简单的应用程序，该应用程序进行连续的
ajax调用，并将第一次调用的结果传递给下一个。

I was working on a simple application that makes sequential ajax calls, passing result of first call into the next one.

我当然不不想进入回调地狱
并因此查看 Promises / A + 规范示例和 Q库。

Of course I don't want to go into the callback hell, and therefore look into Promises/A+ spec example and Q library.

我准备了一个异步函数，应该可以得到我想要的结果。
但是我想了解如何简化顺序承诺的传递。

I have prepared an async function that should result in what I want. But I want an insight on how I can simplify the Sequential promise passing.

到目前为止，我仍在阅读如何最好地处理承诺和延迟对象，因此请原谅
我那非常幼稚的代码。

For now I am still reading on how to best work with promises and deferred objects, so forgive me for the very naive code.

现在我要看两件事：

• 简化承诺顺序的方式（在我的情况下，这取决于一个
  ）



• 建议

• the way to simplify the sequencing of promises (that depend on one another as in my case)

• suggestions

var modifyableObject = {
    toProcess : ["one", "two", "three", "four", "five"]
}


function returnsDeferredResults(someResult) {

    var deferred = Q.defer();

    // my async function (setTimeout for now will do, $.ajax() later)
    setTimeout(function () {

        var nextResult = (someResult || " Initial_Blank_Value ") + "..." + modifyableObject.toProcess[0]; 

        modifyableObject.toProcess = modifyableObject.toProcess.splice(1);

        console.log("New Tick Result: ", nextResult, "Array: ", modifyableObject.toProcess);

        deferred.resolve( nextResult);

    }, 200);

    return deferred.promise;
}


//$("#test_promise").click(function () {

    function getDeferredResult(prevResult) {
        return returnsDeferredResults(prevResult);
    }

    var prevResult = getDeferredResult();

    var nextTick = "";

    for (var i = modifyableObject.toProcess.length; i > 1; i --) {

        if (nextTick) 
            nextTick = nextTick.then(getDeferredResult);
        else 
            nextTick = prevResult.then(getDeferredResult);
    }

    //nextTick.fin(function(){ ...});

//});



/*
New Tick Result:   Initial_Blank_Value ...one           Array:  ["two", "three", "four", "five"]
New Tick Result:   Initial_Blank_Value ...one...two            Array:  ["three", "four", "five"]
New Tick Result:   Initial_Blank_Value ...one...two...three             Array:  ["four", "five"] 
New Tick Result:   Initial_Blank_Value ...one...two...three...four              Array:  ["five"]
New Tick Result:   Initial_Blank_Value ...one...two...three...four...five             Array:  [] 
*/

谢谢大家！

推荐答案

您可以通过组合两个变量来简化循环：

You can simplify your loop by combining the two variables:

var nextTick = getDeferredResult();

for (var i = modifyableObject.toProcess.length; i > 1; i --) {
    nextTick = nextTick.then(getDeferredResult);
}

或者，

return modifyableObject.toProcess.reduce(function(promise, item) {
    return promise.then(getDeferredResult);
}, Q.resolve());

---

您也可以简化功能：

---

You can simplify your function too:

return Q.delay(200).then(function) { 
    return "..." + modifyableObject.toProcess.shift();
});

jQuery AJAX还返回一个承诺，该承诺与Q兼容（在最新版本的jQuery中）

jQuery AJAX also returns a promise, which Q is compatible with (in recent versions of jQuery)

然后可以通过将每个项目传递给函数来组合这两项改进：

You can then combine the two improvements by passing each item to the function:

return modifyableObject.toProcess.reduce(function(promise, item) {
    return promise.then(processItem.bind(null, item));
}, Q.resolve());

function processItem(item) {
    return Q.delay(200).then(function) { 
        return "..." + modifyableObject.toProcess.shift();
    });
}

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