path: root/files/zh-cn/web/javascript/reference/global_objects/promise/all/index.html

---
title: Promise.all()
slug: Web/JavaScript/Reference/Global_Objects/Promise/all
tags:
  - AJAX
  - Async-Await
  - Fetch
  - Promise
  - Promise.all()
  - Promise.race()
  - promise.all
translation_of: Web/JavaScript/Reference/Global_Objects/Promise/all
---
<div>{{JSRef}}</div>

<p>Promise.all() 方法接收一个promise的idterable类型（注：Array，Map，Set都属于ES6的iterable类型）的输入，并且只返回一个{{jsxref("Promise")}}实例， 那个输入的所有promise的resolve回调的结果是一个数组。这个{{jsxref("Promise")}}的resolve回调执行是在所有输入的promise的resolve回调都结束，或者输入的iterable里没有promise了的时候。它的reject回调执行是，只要任何一个输入的promise的reject回调执行或者输入不合法的promise就会立即抛出错误，并且reject的是第一个抛出的错误信息。</p>

<div>{{EmbedInteractiveExample("pages/js/promise-all.html")}}</div>

<p class="hidden">The source for this interactive demo is stored in a GitHub repository. If you'd like to contribute to the interactive demo project, please clone <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox notranslate"><var>Promise.all(iterable)</var>;</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt>iterable</dt>
 <dd>一个<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol">可迭代</a>对象，如 {{jsxref("Array")}} 或 {{jsxref("String")}}。</dd>
</dl>

<h3 id="返回值">返回值</h3>

<ul>
 <li>如果传入的参数是一个空的可迭代对象，则返回一个<strong>已完成（already resolved）</strong>状态的 {{jsxref("Promise")}}。</li>
 <li>如果传入的参数不包含任何 <code>promise</code>，则返回一个<strong>异步完成（asynchronously resolved）</strong> {{jsxref("Promise")}}。注意：Google Chrome 58 在这种情况下返回一个<strong>已完成（already resolved）</strong>状态的 {{jsxref("Promise")}}。</li>
 <li>其它情况下返回一个<strong>处理中（pending）</strong>的{{jsxref("Promise")}}。这个返回的 <code>promise</code> 之后会在所有的 <code>promise</code> 都完成或有一个 <code>promise</code> 失败时<strong>异步</strong>地变为完成或失败。 见下方关于“Promise.all 的异步或同步”示例。返回值将会按照参数内的 <code>promise</code> 顺序排列，而不是由调用 <code>promise</code> 的完成顺序决定。</li>
</ul>

<h2 id="说明">说明</h2>

<p>此方法在集合多个 <code>promise</code> 的返回结果时很有用。</p>

<p>完成（Fulfillment）：<br>
 如果传入的可迭代对象为空，<code>Promise.all</code> 会同步地返回一个已完成（resolved）状态的<code>promise</code>。<br>
 如果所有传入的 <code>promise</code> 都变为完成状态，或者传入的可迭代对象内没有 <code>promise</code>，<code>Promise.all</code> 返回的 <code>promise</code> 异步地变为完成。<br>
 在任何情况下，<code>Promise.all</code> 返回的 <code>promise</code> 的完成状态的结果都是一个数组，它包含所有的传入迭代参数对象的值（也包括非 <code>promise</code> 值）。</p>

<p>失败/拒绝（Rejection）：<br>
 如果传入的 <code>promise</code> 中有一个失败（rejected），<code>Promise.all</code> 异步地将失败的那个结果给失败状态的回调函数，而不管其它 <code>promise</code> 是否完成。</p>

<h2 id="示例">示例</h2>

<h3 id="Promise.all_的使用"><code>Promise.all</code> 的使用</h3>

<p><code>Promise.all</code> 等待所有都完成（或第一个失败）。</p>

<pre class="brush: js notranslate">var p1 = Promise.resolve(3);
var p2 = 1337;
var p3 = new Promise((resolve, reject) =&gt; {
  setTimeout(resolve, 100, 'foo');
});

Promise.all([p1, p2, p3]).then(values =&gt; {
  console.log(values); // [3, 1337, "foo"]
});</pre>

<p>如果参数中包含非 <code>promise</code> 值，这些值将被忽略，但仍然会被放在返回数组中（如果 <code>promise</code> 完成的话）：</p>

<pre class="brush: js notranslate">// this will be counted as if the iterable passed is empty, so it gets fulfilled
var p = Promise.all([1,2,3]);
// this will be counted as if the iterable passed contains only the resolved promise with value "444", so it gets fulfilled
var p2 = Promise.all([1,2,3, Promise.resolve(444)]);
// this will be counted as if the iterable passed contains only the rejected promise with value "555", so it gets rejected
var p3 = Promise.all([1,2,3, Promise.reject(555)]);

// using setTimeout we can execute code after the stack is empty
setTimeout(function(){
    console.log(p);
    console.log(p2);
    console.log(p3);
});

// logs
// Promise { &lt;state&gt;: "fulfilled", &lt;value&gt;: Array[3] }
// Promise { &lt;state&gt;: "fulfilled", &lt;value&gt;: Array[4] }
// Promise { &lt;state&gt;: "rejected", &lt;reason&gt;: 555 }</pre>

<h3 id="Promise.all_的异步和同步"><code>Promise.all</code> 的异步和同步</h3>

<p>下面的例子中演示了 <code>Promise.all</code> 的异步性（如果传入的可迭代对象是空的，就是同步）：</p>

<pre class="brush: js notranslate">// we are passing as argument an array of promises that are already resolved,
// to trigger Promise.all as soon as possible
var resolvedPromisesArray = [Promise.resolve(33), Promise.resolve(44)];

var p = Promise.all(resolvedPromisesArray);
// immediately logging the value of p
console.log(p);

// using setTimeout we can execute code after the stack is empty
setTimeout(function(){
    console.log('the stack is now empty');
    console.log(p);
});

// logs, in order:
// Promise { &lt;state&gt;: "pending" }
// the stack is now empty
// Promise { &lt;state&gt;: "fulfilled", &lt;value&gt;: Array[2] }
</pre>

<p>如果 <code>Promise.all</code> 失败，也是一样的：</p>

<pre class="brush: js notranslate">var mixedPromisesArray = [Promise.resolve(33), Promise.reject(44)];
var p = Promise.all(mixedPromisesArray);
console.log(p);
setTimeout(function(){
    console.log('the stack is now empty');
    console.log(p);
});

// logs
// Promise { &lt;state&gt;: "pending" }
// the stack is now empty
// Promise { &lt;state&gt;: "rejected", &lt;reason&gt;: 44 }
</pre>

<p>但是，<code>Promise.all</code> <strong>当且仅当</strong>传入的可迭代对象为空时为同步：</p>

<pre class="brush: js notranslate">var p = Promise.all([]); // will be immediately resolved
var p2 = Promise.all([1337, "hi"]); // non-promise values will be ignored, but the evaluation will be done asynchronously
console.log(p);
console.log(p2)
setTimeout(function(){
    console.log('the stack is now empty');
    console.log(p2);
});

// logs
// Promise { &lt;state&gt;: "fulfilled", &lt;value&gt;: Array[0] }
// Promise { &lt;state&gt;: "pending" }
// the stack is now empty
// Promise { &lt;state&gt;: "fulfilled", &lt;value&gt;: Array[2] }
</pre>

<h3 id="Promise.all_的快速返回失败行为"><code>Promise.all</code> 的快速返回失败行为</h3>

<p><code>Promise.all</code> 在任意一个传入的 <code>promise</code> 失败时返回失败。例如，如果你传入的 <code>promise</code>中，有四个 <code>promise</code> 在一定的时间之后调用成功函数，有一个立即调用失败函数，那么 <code>Promise.all</code> 将立即变为失败。</p>

<pre class="brush: js notranslate">var p1 = new Promise((resolve, reject) =&gt; {
  setTimeout(resolve, 1000, 'one');
});
var p2 = new Promise((resolve, reject) =&gt; {
  setTimeout(resolve, 2000, 'two');
});
var p3 = new Promise((resolve, reject) =&gt; {
  setTimeout(resolve, 3000, 'three');
});
var p4 = new Promise((resolve, reject) =&gt; {
  setTimeout(resolve, 4000, 'four');
});
var p5 = new Promise((resolve, reject) =&gt; {
  reject('reject');
});

Promise.all([p1, p2, p3, p4, p5]).then(values =&gt; {
  console.log(values);
}, reason =&gt; {
  console.log(reason)
});

//From console:
//"reject"

//You can also use .catch
Promise.all([p1, p2, p3, p4, p5]).then(values =&gt; {
  console.log(values);
}).catch(reason =&gt; {
  console.log(reason)
});

//From console:
//"reject"

</pre>

<h2 id="技术规范">技术规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-promise.all', 'Promise.all')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td>Initial definition in an ECMA standard.</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-promise.all', 'Promise.all')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<p class="hidden">To contribute to this compatibility data, please write a pull request against this repository: <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a>.</p>

<p>{{Compat("javascript.builtins.Promise.all")}}</p>

<h2 id="参见">参见</h2>

<ul>
 <li>{{jsxref("Promise")}}</li>
 <li>{{jsxref("Promise.race()")}}</li>
</ul>