[英]Access value that promise .then returns outside of promise
標題說明了一切,我正在使用async-library eachSeries
方法
let
valueOne = null,
validItem = null;
const asyncEachSeries = require('async/eachSeries');
const getContent = function (item) {
contentResponse = fetchContent(item);
return contentResponse;
}
if (recommendationsArr.length > 0) {
asyncEachSeries(recommendationsArr, function (item, callback) {
getApiContent(item).then(function getValidResult(response) {
try {
valueOne = response.content.valueOne || null; //may or may not be present
recommendationsArr.splice(recommendationsArr.indexOf(item), 1);
validItem = item;
console.log("##### valueOne is: ", valueOne); // I get data here
return true;
} catch (err) {
valueOne = null;
return false;
}
});
//I am guessing I need a return statement here, though not sure what
});
console.log("##### Outside promise, valueOne is: ", valueOne); // no data here
// Access valueOne, validItem, recommendationsArr to be able to pass as props for the component
return {
component: <Layout><ComponentName
//pass other non-dependent props
validItem={validItem}
valueOne={valueOne}
recommendationsArr={recommendationsArr}
/></Layout>,
title: `Page Title`,
};
}
return null;
場景: recommendationsArr
是一個項目數組(它的99.9%不為null,但是由於它是一個外部api調用,所以我希望進行檢查)。 其目的是讓值valueOne
, validItem
,和更新recommendationsArr
。
有效性取決於valueOne
的存在,因此,如果valueOne
recommendationsArr[0]
具有有效的valueOne
則無需為數組的其余部分獲取api結果。 我正在使用eachSeries
因為它一次只運行一個異步操作,因此,如果該異步為我提供了有效的結果,那么我就不必遍歷其他項目。
推薦的recommendationsArr = ["blue", "white", "green", "red"]; //usually the array is anywhere between 12-50 elements
樣本: recommendationsArr = ["blue", "white", "green", "red"]; //usually the array is anywhere between 12-50 elements
樣本recommendationsArr = ["blue", "white", "green", "red"]; //usually the array is anywhere between 12-50 elements
recommendationsArr = ["blue", "white", "green", "red"]; //usually the array is anywhere between 12-50 elements
現在,為了能夠將更新的值傳遞給組件,我需要能夠訪問asyncEachSeries
迭代循環之外的try
塊中設置的值。 我知道我將必須return
已處理的/新值,但不確定何時以及如何返回這些值。
與有關異步代碼的任何問題一樣,通常使用callback
函數返回值。 但是eachSeries
不會收集返回值。 您想要的是async.mapSeries
:
async.mapSeries(recommendationsArr, function (item, callback) {
getApiContent(item).then(function (response) {
try {
valueOne = response.content.valueOne || null; //may or may not be present
recommendationsArr.splice(recommendationsArr.indexOf(item), 1);
validItem = item;
callback(null, valueOne); // This is how you return a value
// return true; // return does absolutely nothing
} catch (err) {
valueOne = null;
callback(err, valueOne);
// return false;
}
});
},function (err, result) {
// this is where you can process the result
// note that the result is an array
});
但是,由於您使用的是Promise,因此可以使用async-q
代替,它將caolan的異步庫包裝在Promise中:
var asyncQ = require('async-q');
asyncQ.mapSeries(recommendationsArr, function (item) {
// Note: the return in the line below is important
return getApiContent(item).then(function (response) {
try {
valueOne = response.content.valueOne || null; //may or may not be present
recommendationsArr.splice(recommendationsArr.indexOf(item), 1);
validItem = item;
return valueOne; // this is how you return a value in a promise
} catch (err) {
return null
}
});
})
.then(function(result) {
// you can process the result here
});
我個人更希望重寫代碼並在最后處理結果,因為代碼更簡潔:
asyncQ.mapSeries(recommendationsArr, getApiContent)
.then(function (result) {
for(var i=0;i<result.length;i++) {
var response = result[i];
// do what needs to be done with each response here
}
});
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