数组过滤器的异步或承诺条件 [英] asynchronous or promised condition for array filter

问题描述

我需要根据只能异步检查的条件过滤数组.

I need to filter an array based on a condition that can only be checked asynchronously.

return someList.filter(function(element){ 
   //this part unfortunately has to be asynchronous
})

有没有比我已有的方法更好的使用 promise 的方法?

Is there any nicer way to do it with promises than what I already have?

此代码段使用 Q 作为承诺，但您实际上可以假设任何适当的承诺实施.

This snippet uses Q for promises, but you can actually assume any proper promises implementation.

return q.all(someList.map(function (listElement) {
        return promiseMeACondition(listElement.entryId).then(function (condition) {
            if (condition) {
                return q.fcall(function () {
                    return listElement;
                });
            } else {
                return q.fcall(function(){});
            }
        });
    }));

示例代码将 promise 解析为过滤后的数组，这就是所需的结果.

The example code resolves the promise to a filtered array and that's the desired result.

推荐答案

在像 Bluebird 这样的库中 - 你有像 .map 和 .filter 这样的内置承诺的方法.您的方法通常是正确的.您只是在最后缺少一个 Array.prototype.filter 来删除坏结果" - 例如，使用 BadValue 常量和与其相等的过滤器元素进行解析.

In libraries like Bluebird - you have methods like .map and .filter of promises built in. Your approach is generally correct. You're just missing an Array.prototype.filter at the end removing the "bad results" - for example, resolve with a BadValue constant and filter elements that are equal to it.

var BadValue = {};

return q.all(someList.map(function (listElement) {
        return promiseMeACondition(listElement.entryId).then(function (listElement) {
            return (condition(listElement)) ? listElement : BadValue;
    })).then(function(arr){
            return arr.filter(function(el){ return el !== BadValue; });
    });

与蓝鸟:

  Promise.filter(someList,condition);

当然，您可以将此功能提取到用于 Promise 的通用 filter 函数.

You can of course, extract this functionality to a generic filter function for promises.

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