处理异步功能的同步方式，两层深 [英] Synchronous way of handling asynchronous function, two level deep

问题描述

我正在遍历一个数组，以使用被调用函数internally calls an asynchronous function的返回值更新其值.

I am looping over an array to update its values using returned value from called function which internally calls an asynchronous function.

我需要以同步方式处理异步函数，而异步方法没有被直接调用. 这是复制场景 .

I need to handle asynchronous function in synchronous way which is not being directly called. This is replication of scenario.

function condition(){
    // Code of this function is not accessible to me.
    return new Promise(function(resolve, reject){
        setTimeout(function(){
            if(parseInt(Math.random() * 100) % 2){
                resolve(true);
            }
            else{
                reject(false)
            }
        }, 1000)
    });
}

async function delayIncrease(value){
    var choice = await condition(); 

    if(choice) { return ++value; }
    else { return --value; }
}

// Start calling functions
dataArr = [1,2,3,4,5];
for(var i in dataArr){
    dataArr[i] = delayIncrease(dataArr[i]);
}

如果可能，我希望采用上述结构的解决方案.

通过adding other function并将"index" + "new_value"作为参数传递，我已经达到了预期的结果.此函数直接modifies original array并产生所需的结果. 工作示例 .

I have achieved the desired result by adding other function and passing "index" + "new_value" as parameters. This function directly modifies original array and produces desired result. Working example.

function condition(){
    // Code of this function is not accessible to me.
    return new Promise(function(resolve, reject){
        setTimeout(function(){
            if(parseInt(Math.random() * 100) % 2){
                resolve(true);
            }
            else{
                reject(false)
            }
        }, 1000)
    });
}

function delayIncrease(value, index){            
    condition().then(
        function(){ updateData(++value, index) },
        function(){ updateData(--value, index) }
    )
}

function updateData(value, index){
    dataArr[index] = value;          
}

dataArr = [1,2,3,4,5];
for(var i in dataArr){
    dataArr[i] = delayIncrease(dataArr[i], i);
}

请以最佳方式提供此要求的解决方案.还提出了Angular 4方式的可能解决方案.我想到了以普通JavaScript形式编写它，因为Observables的行为几乎相同.

Please provide solution for this requirement in best possible way. Possible solution in Angular 4 way is also appriciated. I thought of writing it in normal JavaScript form as Observables behave nearly same.

我关注了此媒体页和 http://exploringjs.com

推荐答案

您的condition函数不能真正实现true或false的诺言，而是随机实现或 reject 的诺言.您需要捕获该错误"，而不是使用布尔值进行分支:

Your condition function does not really fulfill the promise with either true or false, it does randomly fulfill or reject the promise. Instead of branching on a boolean, you will need to catch that "error":

async function delayIncrease(value) {
    try {
        await condition(); 
        return ++value;
    } catch(e) {
        return --value;
    }
}

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