获取异步函数中的上一项

Question

我有三条记录。为了更新每条记录，我需要取上一条记录的值。问题是当方法是异步记录三时，在记录二完成之前开始更新并获得null值。我该如何处理？

const resolvePersons = async (persons) => {
return Promise.all(persons.map(async (person) => {
const data = await getSomePersonData(person);
const value = await getValue(persons); // first person value is statically set
return { data, value };
}));
};
function getSomePersonData(person) {
return new Promise((resolve, reject) => setTimeout(() => resolve({data: someData}), 100);
}
function getValue(persons) {
return new Promise((resolve, reject) => setTimeout(() => resolve(persons[index - 1].value), 100);
}

Answer 1

如果不希望迭代同时运行，请不要使用Promise.all和map。只需写一个await的正常循环：

async function resolvePersons(persons) {
const result = [];
for (const [i, person] of persons.entries()) {
const data = await getSomePersonData(person);
const prevValue = i == 0 ? null : result[i-1].value;
const value = await getValue(prevValue);
result.push({ data, value });
}
return result;
}