Question

我正在研究一个简单的应用程序，它使顺序 ajax调用，将第一次调用的结果传递给下一个调用。

当然，我不想进入回调地狱，因此，请查看Promises/A+规范示例和Q library。

我准备了一个异步函数，它应该导致我想要的东西。但我希望能够深入了解如何简化顺序承诺传递。

目前我还在阅读如何最好地使用promises和deferred对象，所以请原谅我是非常天真的代码。

所以现在我正在研究两件事：

简化承诺排序的方式（取决于一个另一个在我的情况下）

建议

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:  [] 
*/

提前谢谢大家！

Answer 1

您可以通过组合两个变量来简化循环：

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());

您也可以简化您的功能：

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

jQuery AJAX也返回一个承诺，Q与（在最近的jQuery版本中）兼容

然后，您可以通过将每个项目传递给函数来组合这两个改进：

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();
    });
}

如何简化Q promise示例

1 个答案: