使用一些简单的规则非常简单：
还有一些提示：
好的，让我们开始吧：
var items = [1, 2, 3, 4, 5];
var fn = function asyncMultiplyBy2(v){ // sample async action
return new Promise(resolve => setTimeout(() => resolve(v * 2), 100));
};
// map over forEach since it returns
var actions = items.map(fn); // run the function over all items
// we Now have a promises array and we want to wait for it
var results = Promise.all(actions); // pass array of promises
results.then(data => // or just .then(console.log)
console.log(data) // [2, 4, 6, 8, 10]
);
// we can nest this of course, as I said, `then` chains:
var res2 = Promise.all([1, 2, 3, 4, 5].map(fn)).then(
data => Promise.all(data.map(fn))
).then(function(data){
// the next `then` is executed after the promise has returned from the prevIoUs
// `then` fulfilled, in this case it's an aggregate promise because of
// the `.all`
return Promise.all(data.map(fn));
}).then(function(data){
// just for good measure
return Promise.all(data.map(fn));
});
// Now to get the results:
res2.then(function(data){
console.log(data); // [16, 32, 48, 64, 80]
});
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