Question

我有一个遍历对象的递归函数。它查找名称为subcomponent（始终是数组）的键，并在subcomponent的每个子代上执行异步功能，其输出用于替换子代的数据。

在populateSubcomponent()下面的示例中是异步函数。

代码：

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，每个console.log数字应按顺序触发，但我依次得到2，3和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上得到了正确的结果，但是没有传递给2或3。

如何最好地将递归doPopulate()调用与if语句合并？

我看过以下SO帖子：

但是我无法将任何答案与自己的问题相关联，这主要是因为我的递归函数中有一个if语句，但我不确定如何处理在异步内容中。

修改

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);

这一切都发生在NodeJS流中（使用through2），我还需要使流功能也异步：

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);
});

Answer 1

只要下一个诺言依赖于前一个诺言，您就必须顺序等待每个诺言。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。顺便说一句，如果您需要使用async，则只需要await关键字。否则，没有理由制作函数async。

如果您要顺序等待每个诺言，您将像这样重写它：

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;
    });
}

Answer 2

结果证明，我需要按照评论中@Bergi的建议归还两套承诺：

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);

这一切都发生在NodeJS流中（使用through2），我还需要使流功能也异步：

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);
});

NodeJS-在Array.map中使用带有'if'语句的Async / Await

2 个答案: