解决承诺后如何从Promise对象获取值 [英] How to fetch value from Promise object after promise has been resolved

问题描述

请注意，这是一个人为的示例.

Please note This is a contrived example.

    function longFunc(){
        var deferred = $.Deferred();

        setTimeout(function(){
            console.log("long func completed");
            deferred.resolve("hello");
        }, 3000);

        return deferred.promise();
    }

    function shortAfterLongFunc(x){
        console.log('short func completed with value: ' + x);
        return {
            a: x
        };
    }

processFurther(longFunc().then(shortAfterLongFunc)); // send the array for further processing

问题

在shortAfterLongFunc完成后，我无法弄清 如何返回任何类型的对象/函数 .我可以从shortAfterLongFunc进行console.log，但这不是我所需要的. 在这里拨弄

I am unable to figure out how to return any kind of object/function for further downstream processing after shortAfterLongFunc completes. I can console.log from shortAfterLongFunc but that's not what i require here. Fiddle Here

感谢您的光临！

更新:

好的，只是让我的问题稍微好一点...这是我正在研究的一个简单用例:

Okay just to make my question slightly better...this is a simple use case I am looking at:

$.map(['H','E','L','L', 'O'], somefunc). // for each item in array apply somefunc function

function somefunc(x){ // gets called for each value 'H', 'E' etc. in the array by $.map()
    var longfunc = function(y){
        var deferred = $.Deferred();

        setTimeout(function(){
            console.log("long func completed");
            deferred.resolve(y.toLocaleLowerCase());
        }, 3000);

        return deferred.promise();
    };

    var shortAfterLongFunc = function(x){
        console.log('short func completed with value: ' + x);
        return x;
    }

    // What should I do here
    return longFunc(x).then(shortAfterLongFunc); // must return lower case char to the caller of someFunc

}

somefunc()可以说将Array的每个元素处理为小写.但是，假设此处理需要很长时间并且是异步的(请考虑setTimeout)，因此保证了每个元素的同步操作...但是在使用promise时，我发现自己无法返回转换后的值

somefunc() lets say processes each element of Array to lower case. However, assume this processing takes a long time and async (think setTimeout).. hence a promise to ensure synchronous operation for each element...but on using promise I find myself not able return the transformed value

推荐答案

只需链接另一个then调用，因为shortAfterLongFunc返回新的Promise，您可以进一步使用它:

Just chain another then call, since shortAfterLongFunc returns new promise you can further work with it:

longFunc().then(shortAfterLongFunc).then(function(data) {
    console.log('all is complted', data);
});

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