您可以使用归约而不是映射来实现此目的：
stats.reduce(
(chain, item) =>
// append the promise creating function to the chain
chain.then(() => playersApi.getOrAddPlayer(item, clubInfo, year)),
// start the promise chain from a resolved promise
Promise.resolve()
).then(() =>
// all finished, one after the other
);
演示：
const timeoutPromise = x => {
console.log(`starting ${x}`);
return new Promise(resolve => setTimeout(() => {
console.log(`resolving ${x}`);
resolve(x);
}, Math.random() * 2000));
};
[1, 2, 3].reduce(
(chain, item) => chain.then(() => timeoutPromise(item)),
Promise.resolve()
).then(() =>
console.log('all finished, one after the other')
);
如果需要累加值，可以通过归约传播结果：
stats
.reduce(
(chain, item) =>
// append the promise creating function to the chain
chain.then(results =>
playersApi.getOrAddPlayer(item, clubInfo, year).then(data =>
// concat each result from the api call into an array
results.concat(data)
)
),
// start the promise chain from a resolved promise and results array
Promise.resolve([])
)
.then(results => {
// all finished, one after the other
// results array contains the resolved value from each promise
});
演示：
const timeoutPromise = x => {
console.log(`starting ${x}`);
return new Promise(resolve =>
setTimeout(() => {
console.log(`resolving result for ${x}`);
resolve(`result for ${x}`);
}, Math.random() * 2000)
);
};
function getStuffInOrder(initialStuff) {
return initialStuff
.reduce(
(chain, item) =>
chain.then(results =>
timeoutPromise(item).then(data => results.concat(data))
),
Promise.resolve([])
)
}
getStuffInOrder([1, 2, 3]).then(console.log);
变体 #1：Array.prototype.concat 看起来更优雅，但会在每个连接上创建一个新数组。为了提高效率，您可以使用 Array.prototype.push 和更多样板：
stats
.reduce(
(chain, item) =>
chain.then(results =>
playersApi.getOrAddPlayer(item, clubInfo, year).then(data => {
// push each result from the api call into an array and return the array
results.push(data);
return results;
})
),
Promise.resolve([])
)
.then(results => {
});
演示：
const timeoutPromise = x => {
console.log(`starting ${x}`);
return new Promise(resolve =>
setTimeout(() => {
console.log(`resolving result for ${x}`);
resolve(`result for ${x}`);
}, Math.random() * 2000)
);
};
function getStuffInOrder(initialStuff) {
return initialStuff
.reduce(
(chain, item) =>
chain.then(results =>
timeoutPromise(item).then(data => {
results.push(data);
return results;
})
),
Promise.resolve([])
);
}
getStuffInOrder([1, 2, 3]).then(console.log);
变体 #2：您可以将 results 变量提升到上限范围。这将消除嵌套函数的需要，以便在累积数据时通过最近的闭包使results 可用，而是使其对整个链全局可用。
const results = [];
stats
.reduce(
(chain, item) =>
chain
.then(() => playersApi.getOrAddPlayer(item, clubInfo, year))
.then(data => {
// push each result from the api call into the globally available results array
results.push(data);
}),
Promise.resolve()
)
.then(() => {
// use results here
});
演示：
const timeoutPromise = x => {
console.log(`starting ${x}`);
return new Promise(resolve =>
setTimeout(() => {
console.log(`resolving result for ${x}`);
resolve(`result for ${x}`);
}, Math.random() * 2000)
);
};
function getStuffInOrder(initialStuff) {
const results = [];
return initialStuff.reduce(
(chain, item) =>
chain
.then(() => timeoutPromise(item))
.then(data => {
results.push(data);
return results;
}),
Promise.resolve()
);
}
getStuffInOrder([1, 2, 3]).then(console.log);