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author | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
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committer | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
commit | 33058f2b292b3a581333bdfb21b8f671898c5060 (patch) | |
tree | 51c3e392513ec574331b2d3f85c394445ea803c6 /files/zh-cn/web/javascript/reference/global_objects/promise/resolve | |
parent | 8b66d724f7caf0157093fb09cfec8fbd0c6ad50a (diff) | |
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diff --git a/files/zh-cn/web/javascript/reference/global_objects/promise/resolve/index.html b/files/zh-cn/web/javascript/reference/global_objects/promise/resolve/index.html new file mode 100644 index 0000000000..607fa09f36 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/promise/resolve/index.html @@ -0,0 +1,158 @@ +--- +title: Promise.resolve() +slug: Web/JavaScript/Reference/Global_Objects/Promise/resolve +tags: + - ECMAScript 2015 + - JavaScript + - Promise +translation_of: Web/JavaScript/Reference/Global_Objects/Promise/resolve +--- +<div>{{JSRef}}</div> + +<div><code><strong>Promise.resolve(value)</strong></code>方法返回一个以给定值解析后的{{jsxref("Promise")}} 对象。如果这个值是一个 promise ,那么将返回这个 promise ;如果这个值是thenable(即带有{{jsxref("Promise.then", "\"then\" ")}}方法),返回的promise会“跟随”这个thenable的对象,采用它的最终状态;否则返回的promise将以此值完成。<span style="font-size: 1rem; letter-spacing: -0.00278rem;">此函数将类promise对象的多层嵌套展平。</span></div> + +<div></div> + +<div></div> + +<div class="blockIndicator warning"> +<p>警告:不要在解析为自身的thenable 上调用<code>Promise.resolve</code>。这将导致无限递归,因为它试图展平无限嵌套的promise。一个例子是将它与Angular中的异步管道一起使用。在<a href="https://angular.io/guide/template-syntax#avoid-side-effects">此处</a>了解更多信息。</p> +</div> + +<div>{{EmbedInteractiveExample("pages/js/promise-resolve.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="Syntax" name="Syntax">语法</h2> + +<pre class="syntaxbox"><var>Promise.resolve(value)</var>; +</pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt>value</dt> +</dl> + +<p>将被<code>Promise</code>对象解析的参数,也可以是一个<code>Promise</code>对象,或者是一个thenable。</p> + +<h3 id="返回值">返回值</h3> + +<p>返回一个带着给定值解析过的<code>Promise</code>对象,如果参数本身就是一个<code>Promise</code>对象,则直接返回这个<code>Promise</code>对象。</p> + +<h2 id="Description" name="Description">描述</h2> + +<p>静态方法 <code>Promise.resolve</code>返回一个解析过的<code>Promise</code>对象。</p> + +<h2 id="示例">示例</h2> + +<h3 id="使用静态Promise.resolve方法">使用静态<code>Promise.resolve</code>方法</h3> + +<pre class="brush: js">Promise.resolve("Success").then(function(value) { + console.log(value); // "Success" +}, function(value) { + // 不会被调用 +}); +</pre> + +<h3 id="resolve一个数组">resolve一个数组</h3> + +<pre class="brush: js">var p = Promise.resolve([1,2,3]); +p.then(function(v) { + console.log(v[0]); // 1 +}); +</pre> + +<h3 id="resolve另一个promise">resolve另一个promise</h3> + +<pre class="brush: js">var original = Promise.resolve(33); +var cast = Promise.resolve(original); +cast.then(function(value) { + console.log('value: ' + value); +}); +console.log('original === cast ? ' + (original === cast)); + +/* +* 打印顺序如下,这里有一个同步异步先后执行的区别 +* original === cast ? true +* value: 33 +*/</pre> + +<p>日志顺序颠倒其实是由于异步地调用<code>then</code> 方法。在<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then#Return_value">这里</a>查看<code>then</code> 是如何工作的。</p> + +<h3 id="resolve_thenable_并抛出错误">resolve thenable 并抛出错误</h3> + +<pre class="brush: js">// Resolve一个thenable对象 +var p1 = Promise.resolve({ + then: function(onFulfill, onReject) { onFulfill("fulfilled!"); } +}); +console.log(p1 instanceof Promise) // true, 这是一个Promise对象 + +p1.then(function(v) { + console.log(v); // 输出"fulfilled!" + }, function(e) { + // 不会被调用 +}); + +// Thenable在callback之前抛出异常 +// Promise rejects +var thenable = { then: function(resolve) { + throw new TypeError("Throwing"); + resolve("Resolving"); +}}; + +var p2 = Promise.resolve(thenable); +p2.then(function(v) { + // 不会被调用 +}, function(e) { + console.log(e); // TypeError: Throwing +}); + +// Thenable在callback之后抛出异常 +// Promise resolves +var thenable = { then: function(resolve) { + resolve("Resolving"); + throw new TypeError("Throwing"); +}}; + +var p3 = Promise.resolve(thenable); +p3.then(function(v) { + console.log(v); // 输出"Resolving" +}, function(e) { + // 不会被调用 +}); +</pre> + +<h2 id="规范">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('ES6', '#sec-promise.resolve', 'Promise.resolve')}}</td> + <td>{{Spec2('ES6')}}</td> + <td>ECMA标准中的首次定义</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-promise.resolve', 'Promise.resolve')}}</td> + <td>{{Spec2('ES6')}}</td> + <td></td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + +<p class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p> + +<p>{{Compat("javascript.builtins.Promise.resolve")}}</p> + +<h2 id="参见">参见</h2> + +<ul> + <li>{{jsxref("Promise")}}</li> +</ul> |