Promise.all：解析值的顺序

看着MDN https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all它看起来像values传递给then()Promise.all 的回调包含按照 Promise 顺序排列的值。例如：

var somePromises = [1, 2, 3, 4, 5].map(Promise.resolve);
return Promise.all(somePromises).then(function(results) {
  console.log(results) //  is [1, 2, 3, 4, 5] the guaranteed result?
});

任何人都可以引用说明顺序的规范values应该在？

PS：运行这样的代码表明这似乎是正确的，尽管这当然没有证据 - 这可能是巧合。

不久，订单被保留 https://www.karltarvas.com/2015/01/21/order-of-resolved-values-in-promise-all.html.

按照您链接到的规范，Promise.all(iterable) https://tc39.es/ecma262/#sec-promise.all需要一个iterable https://tc39.es/ecma262/#sec-iterator-interface作为参数并内部调用PerformPromiseAll(iterator, constructor, resultCapability) https://tc39.es/ecma262/#sec-performpromiseall与它一起，后者循环iterable using IteratorStep(iterator) https://tc39.es/ecma262/#sec-iteratorstep.

解决是通过实现Promise.all() Resolve https://tc39.es/ecma262/#sec-promise.all-resolve-element-functions每个已解决的承诺都有一个内部[[Index]]slot，它标记原始输入中promise的索引。

所有这些意味着输出是严格排序的，因为您传递给 Promise.all() 的可迭代对象是严格排序的（例如，数组）。

您可以在下面的小提琴（ES6）中看到它的实际效果：

// Used to display results
const write = msg => {
  document.body.appendChild(document.createElement('div')).innerHTML = msg;
};

// Different speed async operations
const slow = new Promise(resolve => {
  setTimeout(resolve, 200, 'slow');
});
const instant = 'instant';
const quick = new Promise(resolve => {
  setTimeout(resolve, 50, 'quick');
});

// The order is preserved regardless of what resolved first
Promise.all([slow, instant, quick]).then(responses => {
  responses.map(response => write(response));
});