[英]NodeJS - Using Async/Await inside Array.map with 'if' statement
我有一个遍历对象的递归函数。 它寻找名称为subcomponent
键(始终是一个数组),并对每个subcomponent
的子代执行异步功能,其输出用于替换子代的数据。
在下面的示例中, populateSubcomponent()
是异步函数。
码:
async function doPopulate(data) {
Object.keys(data).map((key) => {
if (typeof data[key] === 'object') { // We want to do a recursive check on the data so are interested in any objects (arrays) at this point
if (key === 'subcomponent') { // If we have an object (array) with key `subcomponent` we want to populate each of its children
const promises = data[key].map(subcomponent => populateSubcomponent(subcomponent));
return Promise.all(promises).then((output) => {
data[key] = output;
console.log('1');
});
}
doPopulate(data[key]); // Check recursively
console.log('2');
}
console.log('3');
return data;
});
}
doPopulate(data);
我的期望是每一个的console.log
号应该依次开火,而是我得到2
, 3
,然后1
。 结果,递归函数在异步函数完成之前运行,因此永远不要按预期替换子级。 我在1
处得到正确的结果,但未传递给2
或3
。
如何最好地将递归doPopulate()
调用与if
语句合并在一起?
我看过以下SO帖子:
但我无法将任何答案与自己的问题相关联,这主要是由于以下事实:我在递归函数中有一个if
语句,而且我不确定如何在异步内容中处理该问题。
编辑
感谢大家的评论,我提出了以下建议:
async function doPopulate(data) {
const promisesOuter = Object.keys(data).map(async (key) => {
if (typeof data[key] === 'object') { // We want to do a recursive check on the data so are interested in any objects (arrays) at this point
if (key === 'subcomponent') { // If we have an object (array) with key `subcomponent` we want to populate each of its children
const promisesInner = data[key].map(subcomponent => populateSubcomponent(subcomponent));
data[key] = await Promise.all(promisesInner);
}
await doPopulate(data[key]); // Check recursively
}
return data;
});
return Promise.all(promisesOuter);
}
return doPopulate(data);
由于这一切都发生在NodeJS流中(使用through2 ),所以我还需要使流功能异步:
const through = require('through2');
return through.obj(async (file, enc, done) => {
const data = JSON.parse(file.contents.toString());
await doPopulate(data);
file.contents = Buffer.from(JSON.stringify(data));
return done(null, file);
});
只要下一个承诺依赖于前一个承诺,您就必须顺序等待每个承诺。 如果可以同时完成它们,则只需汇总承诺并与Promise.all
一起等待它们。 顺便说一下,如果需要使用await
则只需要async
关键字。 否则,没有理由使函数async
。
如果您想顺序等待每个诺言,则可以这样重写它:
function doPopulate(data) {
return Object.keys(data).map(async (key) => {
if (typeof data[key] === 'object') { // We want to do a recursive check on the data so are interested in any objects (arrays) at this point
if (key === 'subcomponent') { // If we have an object (array) with key `subcomponent` we want to populate each of its children
const promises = data[key].map((subcomponent) =>
populateSubcomponent(subcomponent)
);
data[key] = await Promise.all(promises);
console.log('1');
}
await doPopulate(data[key]); // Check recursively
console.log('2');
}
console.log('3');
return data;
});
}
事实证明,我需要返回两组诺言,如@Bergi在评论中建议的那样:
async function doPopulate(data) {
const promisesOuter = Object.keys(data).map(async (key) => {
if (typeof data[key] === 'object') { // We want to do a recursive check on the data so are interested in any objects (arrays) at this point
if (key === 'subcomponent') { // If we have an object (array) with key `subcomponent` we want to populate each of its children
const promisesInner = data[key].map(subcomponent => populateSubcomponent(subcomponent));
data[key] = await Promise.all(promisesInner);
}
await doPopulate(data[key]); // Check recursively
}
return data;
});
return Promise.all(promisesOuter);
}
return doPopulate(data);
由于这一切都发生在NodeJS流中(使用through2 ),所以我还需要使流功能异步:
return through.obj(async (file, enc, done) => {
const data = JSON.parse(file.contents.toString());
await doPopulate(data);
file.contents = Buffer.from(JSON.stringify(data));
return done(null, file);
});
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