entityMap|blocks|key|2hoho|text|promise库如何决定|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5moqf|如果它有一个|2439i|函数-这是|4oebv|仅限|eph9n|使用标准promise库。|8gbg1|Promises/A%2B规范有一个概念，称为|b6fsc|它基本上就是“一个对象，它有一个|b6nr7|方法“。承诺将并且应该被同化|7rc6h|任何事|cdu6a|使用then方法。你提到的所有promise实现都是这样做的。|22kc0|如果我们看一下|e8or6|规格|d4hmo|2.3.3.3如果|8g6q|是一个函数，调用它时使用x作为this，第一个参数为resolvePromise，第二个参数为rejectPromise|603d3|ua1b|它还解释了此设计决策的基本原理：|8i1ek|这种处理方式|b59rf|ables允许promise实现进行互操作，只要它们公开符合Promises/A%2B的|c0th|方法。它还允许Promises/A%2B实现用合理的then方法“同化”不符合规范的实现。|8tnp2|j1jl|你应该如何决定|8f49a|你不应该-而是打电话给|eokai|(|e37h1|在Q)中，将|1iadr|始终|3ppt0|转换任何值或外部|16dda|能够成为一个值得信赖的承诺。这比自己执行这些检查更安全、更容易。|40e5i|真的吗|3gb39|需要确认吗？|e4u3s|你可以随时运行它|9a4e9|测试套件|a5ikh|:D^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|20|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|21|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|22|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|23|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|24|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|25|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|26|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|27|9|@]|A|@]|B|$]]|$2|Q|4|R|6|7|8|28|9|@]|A|@]|B|$]]|$2|S|4|T|6|7|8|29|9|@]|A|@]|B|$]]|$2|U|4|V|6|7|8|2A|9|@]|A|@]|B|$]]|$2|W|4|X|6|7|8|2B|9|@]|A|@]|B|$]]|$2|Y|4|Z|6|7|8|2C|9|@]|A|@]|B|$]]|$2|10|4|11|6|7|8|2D|9|@]|A|@]|B|$]]|$2|12|4|-4|6|7|8|2E|9|@]|A|@]|B|$]]|$2|13|4|14|6|7|8|2F|9|@]|A|@]|B|$]]|$2|15|4|16|6|7|8|2G|9|@]|A|@]|B|$]]|$2|17|4|18|6|7|8|2H|9|@]|A|@]|B|$]]|$2|19|4|1A|6|7|8|2I|9|@]|A|@]|B|$]]|$2|1B|4|-4|6|7|8|2J|9|@]|A|@]|B|$]]|$2|1C|4|1D|6|7|8|2K|9|@]|A|@]|B|$]]|$2|1E|4|1F|6|7|8|2L|9|@]|A|@]|B|$]]|$2|1G|4|1H|6|7|8|2M|9|@]|A|@]|B|$]]|$2|1I|4|1J|6|7|8|2N|9|@]|A|@]|B|$]]|$2|1K|4|1L|6|7|8|2O|9|@]|A|@]|B|$]]|$2|1M|4|1N|6|7|8|2P|9|@]|A|@]|B|$]]|$2|1O|4|1P|6|7|8|2Q|9|@]|A|@]|B|$]]|$2|1Q|4|1R|6|7|8|2R|9|@]|A|@]|B|$]]|$2|1S|4|1T|6|7|8|2S|9|@]|A|@]|B|$]]|$2|1U|4|1V|6|7|8|2T|9|@]|A|@]|B|$]]|$2|1W|4|1X|6|7|8|2U|9|@]|A|@]|B|$]]|$2|1Y|4|1Z|6|7|8|2V|9|@]|A|@]|B|$]]]]

<h2>How a promise library decides</h2>
If it has a <code>.then</code> function - that's the only standard promise libraries use.
The Promises/A+ specification has a notion called <code>then</code>able which is basically &quot;an object with a <code>then</code> method&quot;. Promises will and should assimilate anything with a then method. All of the promise implementation you've mentioned do this.
If we look at the <a href="https://promisesaplus.com/#point-53" rel="noreferrer">specification</a>:
<blockquote>
2.3.3.3 if <code>then</code> is a function, call it with x as this, first argument resolvePromise, and second argument rejectPromise
</blockquote>
It also explains the rationale for this design decision:
<blockquote>
This treatment of <code>then</code>ables allows promise implementations to interoperate, as long as they expose a Promises/A+-compliant <code>then</code> method. It also allows Promises/A+ implementations to “assimilate” nonconformant implementations with reasonable then methods.
</blockquote>
<h2>How you should decide</h2>
You shouldn't - instead call <code>Promise.resolve(x)</code> (<code>Q(x)</code> in Q) that will always convert any value or external <code>then</code>able into a trusted promise. It is safer and easier than performing these checks yourself.
<h3>really need to be sure?</h3>
You can always run it through <a href="https://github.com/promises-aplus/promises-tests" rel="noreferrer">the test suite</a> :D

entityMap|blocks|key|bpq2s|text|检查某些内容是否为promise会使代码变得不必要地复杂，只需使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|d88tu|Promise.resolve(valueOrPromiseItDoesntMatter).then(function(value)+{

})|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

Checking if something is promise unnecessarily complicates the code, just use <code>Promise.resolve</code>

<pre><code>Promise.resolve(valueOrPromiseItDoesntMatter).then(function(value) {

})
</code></pre>

entityMap|blocks|key|1fbq|text|if+(typeof+thing?.then+===+'function')+{
++++//+probably+a+promise
}+else+{
++++//+definitely+not+a+promise
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>if (typeof thing?.then === 'function') {
 // probably a promise
} else {
 // definitely not a promise
}
</code></pre>

entityMap|blocks|key|4jn5a|text|查看给定对象是否为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|acfnd|ES6承诺|622sc|，我们可以使用这个谓词：|q8fp|function+isPromise(p)+{
++return+p+&&+Object.prototype.toString.call(p)+===+"[object+Promise]";
}|code-block|syntax|javascript|c22ed|ing|58eff|直接从|83b9q|返回一个|9bfv1|本机字符串表示|c983a|指定的对象类型的|evtcl|在我们的情况下。这确保了给定的对象|289pu|绕过误报，例如..：|3p8c5|具有相同构造函数名称("Promise")的自定义对象类型。|2jvhe|自写|cp51h|方法。|6e4r1|​|91de6|可跨多个环境上下文工作(例如iframes)|a1n7f|与|78b6k|(|43mid|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof#instanceof|1lors|and_multiple_context|7f4js|(e.g._frames_or_windows%2529|63f7m|)或|a3qva|..。|8nvm6|但是，任何特定的|6ipnr|主机对象|fahv2|，这有它的|8lno7|通过以下方式修改的标签|9ip50|，可以返回|206ri|..。这可能是预期的结果，也可能不是，这取决于项目(例如，如果有自定义的Promise实现)。|59n2t|查看对象是否来自|ehuem|原生ES6+Promise|a4soq|，我们可以使用：|5o986|function+isNativePromise(p)+{
++return+p+&&+typeof+p.constructor+===+"function"
++++&&+Function.prototype.toString.call(p.constructor).replace(/$.*$/,+"()")
++++===+Function.prototype.toString.call(/*native+object*/Function)
++++++.replace("Function",+"Promise")+//+replacing+Identifier
++++++.replace(/$.*$/,+"()");+//+removing+possible+FormalParameterList+
}|77cp9|根据|n0qc|这个|85ll|和|2uh51|本节|5g7l9|在规范中，函数的字符串表示形式应为：|7orbg|“函数|4dg7h|标识符|4n1l5|7kitt|FormalParameterListopt|19ops|){|2kemm|FunctionBody|89dk8|}“|2jafe|5uba8|这在上面进行了相应的处理。The+The+The|cfdk8|e9cnd|是|8ca9h|在所有主流浏览器中。|57o2k|MDN：|7k2p9|这也适用于多个环境上下文。^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|36|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|37|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|38|9|@]|A|@]|B|$]]|$2|G|4|H|6|I|8|39|9|@]|A|@]|B|$J|K]]|$2|L|4|M|6|7|8|3A|9|@]|A|@]|B|$]]|$2|N|4|O|6|7|8|3B|9|@]|A|@]|B|$]]|$2|P|4|Q|6|7|8|3C|9|@]|A|@]|B|$]]|$2|R|4|S|6|7|8|3D|9|@]|A|@]|B|$]]|$2|T|4|U|6|7|8|3E|9|@]|A|@]|B|$]]|$2|V|4|W|6|7|8|3F|9|@]|A|@]|B|$]]|$2|X|4|Y|6|7|8|3G|9|@]|A|@]|B|$]]|$2|Z|4|10|6|7|8|3H|9|@]|A|@]|B|$]]|$2|11|4|12|6|7|8|3I|9|@]|A|@]|B|$]]|$2|13|4|14|6|7|8|3J|9|@]|A|@]|B|$]]|$2|15|4|16|6|7|8|3K|9|@]|A|@]|B|$]]|$2|17|4|18|6|7|8|3L|9|@]|A|@]|B|$]]|$2|19|4|1A|6|7|8|3M|9|@]|A|@]|B|$]]|$2|1B|4|1C|6|7|8|3N|9|@]|A|@]|B|$]]|$2|1D|4|1E|6|7|8|3O|9|@]|A|@]|B|$]]|$2|1F|4|1G|6|7|8|3P|9|@]|A|@]|B|$]]|$2|1H|4|1I|6|7|8|3Q|9|@]|A|@]|B|$]]|$2|1J|4|1K|6|7|8|3R|9|@]|A|@]|B|$]]|$2|1L|4|1M|6|7|8|3S|9|@]|A|@]|B|$]]|$2|1N|4|1O|6|7|8|3T|9|@]|A|@]|B|$]]|$2|1P|4|1Q|6|7|8|3U|9|@]|A|@]|B|$]]|$2|1R|4|1S|6|7|8|3V|9|@]|A|@]|B|$]]|$2|1T|4|1U|6|7|8|3W|9|@]|A|@]|B|$]]|$2|1V|4|1W|6|7|8|3X|9|@]|A|@]|B|$]]|$2|1X|4|1Y|6|7|8|3Y|9|@]|A|@]|B|$]]|$2|1Z|4|20|6|7|8|3Z|9|@]|A|@]|B|$]]|$2|21|4|22|6|7|8|40|9|@]|A|@]|B|$]]|$2|23|4|24|6|7|8|41|9|@]|A|@]|B|$]]|$2|25|4|26|6|I|8|42|9|@]|A|@]|B|$J|K]]|$2|27|4|28|6|7|8|43|9|@]|A|@]|B|$]]|$2|29|4|2A|6|7|8|44|9|@]|A|@]|B|$]]|$2|2B|4|2C|6|7|8|45|9|@]|A|@]|B|$]]|$2|2D|4|2E|6|7|8|46|9|@]|A|@]|B|$]]|$2|2F|4|2G|6|7|8|47|9|@]|A|@]|B|$]]|$2|2H|4|2I|6|7|8|48|9|@]|A|@]|B|$]]|$2|2J|4|2K|6|7|8|49|9|@]|A|@]|B|$]]|$2|2L|4|1C|6|7|8|4A|9|@]|A|@]|B|$]]|$2|2M|4|2N|6|7|8|4B|9|@]|A|@]|B|$]]|$2|2O|4|2P|6|7|8|4C|9|@]|A|@]|B|$]]|$2|2Q|4|2R|6|7|8|4D|9|@]|A|@]|B|$]]|$2|2S|4|2T|6|7|8|4E|9|@]|A|@]|B|$]]|$2|2U|4|-4|6|7|8|4F|9|@]|A|@]|B|$]]|$2|2V|4|2W|6|7|8|4G|9|@]|A|@]|B|$]]|$2|2X|4|2R|6|7|8|4H|9|@]|A|@]|B|$]]|$2|2Y|4|2Z|6|7|8|4I|9|@]|A|@]|B|$]]|$2|30|4|31|6|7|8|4J|9|@]|A|@]|B|$]]|$2|32|4|33|6|7|8|4K|9|@]|A|@]|B|$]]|$2|34|4|35|6|7|8|4L|9|@]|A|@]|B|$]]]]

To see if the given object is a ES6 Promise, we can make use of this predicate:

<pre><code>function isPromise(p) {
 return p &amp;&amp; Object.prototype.toString.call(p) === "[object Promise]";
}
</code></pre>

<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call" rel="noreferrer"><code>Call</code></a>ing <code>toString</code> directly from the <code>Object.prototype</code> returns a <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.2" rel="noreferrer">native string representation</a> of the given object type which is <code>"[object Promise]"</code> in our case. This ensures that the given object

<ul>
<li>Bypasses false positives such as..:

<ul>
<li>Self-defined object type with the same constructor name ("Promise").</li>
<li>Self-written <code>toString</code> method of the given object.</li>
</ul></li>
<li>Works across multiple environment contexts (e.g. iframes) <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof#instanceof_and_multiple_context_(e.g._frames_or_windows)" rel="noreferrer">in contrast to <code>instanceof</code></a> or <code>isPrototypeOf</code>.</li>
</ul>

However, any particular <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-4.3.8" rel="noreferrer">host object</a>, that has its <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/toStringTag" rel="noreferrer">tag modified via <code>Symbol.toStringTag</code></a>, can return <code>"[object Promise]"</code>. This may be the intended result or not depending on the project (e.g. if there is a custom Promise implementation).

<hr>

To see if the object is from a native ES6 Promise, we can use:

<pre><code>function isNativePromise(p) {
 return p &amp;&amp; typeof p.constructor === "function"
 &amp;&amp; Function.prototype.toString.call(p.constructor).replace(/$.*$/, "()")
 === Function.prototype.toString.call(/*native object*/Function)
 .replace("Function", "Promise") // replacing Identifier
 .replace(/$.*$/, "()"); // removing possible FormalParameterList 
}
</code></pre>

According to <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-15.3.4.2" rel="noreferrer">this</a> and <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-13" rel="noreferrer">this section</a> of the spec, the string representation of function should be:

<blockquote>
 "function Identifier ( FormalParameterListopt ) { FunctionBody }"
</blockquote>

which is handled accordingly above. The FunctionBody is <code>[native code]</code> in all major browsers.

<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/toString" rel="noreferrer">MDN: <code>Function.prototype.toString</code></a>

This works across multiple environment contexts as well.

entityMap|blocks|key|rt9k|text|这就是为什么|type|unstyled|depth|inlineStyleRanges|entityRanges|data|cmmoe|graphql-js|fpbc0|package检测promises：|7vur7|function+isPromise(value)+{
++return+Boolean(value+&&+typeof+value.then+===+'function');
}|code-block|syntax|javascript|9cuqp|是函数的返回值。我在我的项目中使用了这段代码，到目前为止还没有问题。^0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|N|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|O|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|P|9|@]|A|@]|B|$]]|$2|G|4|H|6|I|8|Q|9|@]|A|@]|B|$J|K]]|$2|L|4|M|6|7|8|R|9|@]|A|@]|B|$]]]]

This is how <a href="https://github.com/graphql/graphql-js/blob/master/src/jsutils/isPromise.js" rel="noreferrer">graphql-js</a> package detects promises:

<pre><code>function isPromise(value) {
 return Boolean(value &amp;&amp; typeof value.then === 'function');
}
</code></pre>

<code>value</code> is the returned value of your function. I'm using this code in my project and have no problem so far.

entityMap|blocks|key|dbdep|text|不是完整问题的答案，但我认为值得一提的是，在Node.js+10中有一个新的util函数，名为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4q1do|添加了检查对象是否是原生Promise的：|ecgt5|const+utilTypes+=+require('util').types
const+b_Promise+=+require('bluebird')

utilTypes.isPromise(Promise.resolve(5))+//+true
utilTypes.isPromise(b_Promise.resolve(5))+//+false|code-block|syntax|javascript^0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|J|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|K|9|@]|A|@]|B|$]]|$2|E|4|F|6|G|8|L|9|@]|A|@]|B|$H|I]]]]

Not an answer to the full question but I think it's worth to mention that in Node.js 10 a new util function called <a href="https://nodejs.org/api/util.html#util_util_types_ispromise_value" rel="noreferrer"><code>isPromise</code></a> was added which checks if an object is a native Promise or not:

<pre><code>const utilTypes = require('util').types
const b_Promise = require('bluebird')

utilTypes.isPromise(Promise.resolve(5)) // true
utilTypes.isPromise(b_Promise.resolve(5)) // false
</code></pre>

entityMap|blocks|key|bbu88|text|如果您使用的是异步方法，则可以执行此操作并避免任何歧义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|ecag4|async+myMethod(promiseOrNot){
++const+theValue+=+await+promiseOrNot()
}|code-block|syntax|javascript|5cvd2|如果函数返回promise，它将等待并返回已解析的值。如果函数返回值，它将被视为已解析。|18o49|如果函数今天不返回promise，但明天返回promise，或者声明为async，则您将是面向未来的。^0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|L|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|M|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|N|9|@]|A|@]|B|$]]|$2|J|4|K|6|7|8|O|9|@]|A|@]|B|$]]]]

If you are in an async method you can do this and avoid any ambiguity.

<pre><code>async myMethod(promiseOrNot){
 const theValue = await promiseOrNot()
}
</code></pre>

If the function returns promise, it will await and return with the resolved value. If the function returns a value, it will be treated as resolved.

If the function does not return a promise today, but tomorrow returns one or is declared async, you will be future-proof.

entityMap|blocks|key|3c5ue|text|这是代码表单|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4pcq0|https://github.com/ssnau/xkit/blob/master/util/is-promise.js|80clr|!!obj+&&+(typeof+obj+===+'object'+%7C%7C+typeof+obj+===+'function')+&&+typeof+obj.then+===+'function';|code-block|syntax|javascript|7dncp|如果一个对象具有|dponl|方法，则应将其视为|8rdps|..。^0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|P|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|Q|9|@]|A|@]|B|$]]|$2|E|4|F|6|G|8|R|9|@]|A|@]|B|$H|I]]|$2|J|4|K|6|7|8|S|9|@]|A|@]|B|$]]|$2|L|4|M|6|7|8|T|9|@]|A|@]|B|$]]|$2|N|4|O|6|7|8|U|9|@]|A|@]|B|$]]]]

Here is the code form <a href="https://github.com/ssnau/xkit/blob/master/util/is-promise.js" rel="noreferrer">https://github.com/ssnau/xkit/blob/master/util/is-promise.js</a>

<pre><code>!!obj &amp;&amp; (typeof obj === 'object' || typeof obj === 'function') &amp;&amp; typeof obj.then === 'function';
</code></pre>

if an object with a <code>then</code> method, it should be treat as a <code>Promise</code>.

entityMap|blocks|key|8cb6h|text|如果您正在使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5vo8a|打字脚本|8ft59|，我想补充的是，你可以使用“类型谓词”特性。只是应该将逻辑验证包装在一个函数中，该函数返回|5vsip|而且你也不需要做类型转换。下面是我的例子，|ef63j|可以是promise，也可以是我想要转换为promise的类型之一，方法是调用|3n5n1|方法。|bkp1u|export+function+toPromise(c:+Container+%7C+Promise):+Promise+{
++++if+(c+==+null)+return+Promise.resolve();
++++return+isContainer(c)+?+c.fetch()+:+c;
}

export+function+isContainer(val:+Container+%7C+Promise):+val+is+Container+{
++++return+val+&&+(>val).fetch+!==+undefined;
}

export+function+isPromise(val:+Container+%7C+Promise):+val+is+Promise+{
++++return+val+&&+(>val).then+!==+undefined;
}|code-block|syntax|javascript|9me2p|更多信息：|5hp4t|https://www.typescriptlang.org/docs/handbook/advanced-types.html^0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|V|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|W|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|X|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|Y|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|Z|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|10|9|@]|A|@]|B|$]]|$2|M|4|N|6|O|8|11|9|@]|A|@]|B|$P|Q]]|$2|R|4|S|6|7|8|12|9|@]|A|@]|B|$]]|$2|T|4|U|6|7|8|13|9|@]|A|@]|B|$]]]]

In case you are using Typescript, I'd like to add that you can use the "type predicate" feature. Just should wrap the logical verification in a function that returns <code>x is Promise&lt;any&gt;</code> and you won't need to do typecasts. Below on my example, <code>c</code> is either a promise or one of my types which I want to convert into a promise by calling the <code>c.fetch()</code> method.

<pre><code>export function toPromise(c: Container&lt;any&gt; | Promise&lt;any&gt;): Promise&lt;any&gt; {
 if (c == null) return Promise.resolve();
 return isContainer(c) ? c.fetch() : c;
}

export function isContainer(val: Container&lt;any&gt; | Promise&lt;any&gt;): val is Container&lt;any&gt; {
 return val &amp;&amp; (&lt;Container&lt;any&gt;&gt;val).fetch !== undefined;
}

export function isPromise(val: Container&lt;any&gt; | Promise&lt;any&gt;): val is Promise&lt;any&gt; {
 return val &amp;&amp; (&lt;Promise&lt;any&gt;&gt;val).then !== undefined;
}
</code></pre>

More info: <a href="https://www.typescriptlang.org/docs/handbook/advanced-types.html" rel="noreferrer">https://www.typescriptlang.org/docs/handbook/advanced-types.html</a>

entityMap|blocks|key|7la7m|text|任何可能推动同步的东西|type|unstyled|depth|inlineStyleRanges|entityRanges|data|33u9v|变成|3lsq4|为了避免比较的舒适，将你的代码变成一个原本可以避免的异步。有时在那个阶段你并不想要它。您想知道在微任务队列中较早的解决方案咬到您之前评估的结果，对吧？|64s5i|一个人可能会这样做；|22n49|var+isPromise+=+x+=>+Object(x).constructor+===+Promise;|code-block|syntax|javascript|pkd3|我根据我能想到的一些边缘情况对它进行了检查，它似乎是有效的。|eo259|isPromise(undefined);+++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise(null);++++++++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise(0);+++++++++++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise("");++++++++++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise({});++++++++++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise(setTimeout);++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise(Promise);+++++++++++++++++++++++++++++++++++++++++++++//+<-+false
isPromise(new+Promise((v,x)+=>+setTimeout(v,1000,"whatever")));+//+<-+true
isPromise(fetch('http://example.com/movies.json'));+++++++++++++//+<-+true|b9hsf|我还没有检查过任何非本地库，但是现在有什么意义呢？^0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|T|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|U|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|V|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|W|9|@]|A|@]|B|$]]|$2|I|4|J|6|K|8|X|9|@]|A|@]|B|$L|M]]|$2|N|4|O|6|7|8|Y|9|@]|A|@]|B|$]]|$2|P|4|Q|6|K|8|Z|9|@]|A|@]|B|$L|M]]|$2|R|4|S|6|7|8|10|9|@]|A|@]|B|$]]]]

Anything that pushes a possibly synch <code>value</code> into <code>Promise.resolve(value)</code> for the comfort of avoiding comparison turns your code into an otherwise avoidable async. Sometimes you don't want it at that stage. You want to know the result evaluated right before some earlier resolution in the microtask queue bites you right..?
One can possibly do like;
<pre><code>var isPromise = x =&gt; Object(x).constructor === Promise;
</code></pre>
I checked it against some edge cases that i can think of and it seems to work.
<pre><code>isPromise(undefined); // &lt;- false
isPromise(null); // &lt;- false
isPromise(0); // &lt;- false
isPromise(&quot;&quot;); // &lt;- false
isPromise({}); // &lt;- false
isPromise(setTimeout); // &lt;- false
isPromise(Promise); // &lt;- false
isPromise(new Promise((v,x) =&gt; setTimeout(v,1000,&quot;whatever&quot;))); // &lt;- true
isPromise(fetch('http://example.com/movies.json')); // &lt;- true
</code></pre>
I haven't checked it up against any non-native librarires but what's the point now?

entityMap|blocks|key|ast6p|text|it('should+return+a+promise',+function()+{
++++var+result+=+testedFunctionThatReturnsPromise();
++++expect(result).toBeDefined();
++++//+3+slightly+different+ways+of+verifying+a+promise
++++expect(typeof+result.then).toBe('function');
++++expect(result+instanceof+Promise).toBe(true);
++++expect(result).toBe(Promise.resolve(result));
});|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>it('should return a promise', function() {
 var result = testedFunctionThatReturnsPromise();
 expect(result).toBeDefined();
 // 3 slightly different ways of verifying a promise
 expect(typeof result.then).toBe('function');
 expect(result instanceof Promise).toBe(true);
 expect(result).toBe(Promise.resolve(result));
});
</code></pre>

entityMap|blocks|key|5f1id|text|在搜索|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2v560|可靠|9kopi|检测方法|8eaib|异步|4gla1|函数，甚至|3h019|承诺|bi5ar|，我最终使用了以下测试：|9mcts|()+=>+fn.constructor.name+===+'Promise'+%7C%7C+fn.constructor.name+===+'AsyncFunction'|code-block|syntax|javascript^0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|T|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|U|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|V|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|W|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|X|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|Y|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|Z|9|@]|A|@]|B|$]]|$2|O|4|P|6|Q|8|10|9|@]|A|@]|B|$R|S]]]]

after searching for a reliable way to detect Async functions or even Promises, i ended up using the following test : 

<pre><code>() =&gt; fn.constructor.name === 'Promise' || fn.constructor.name === 'AsyncFunction'
</code></pre>

entityMap|blocks|key|a8hm8|text|我使用此函数作为通用解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|bui9i|function+isPromise(value)+{
++return+value+&&+value.then+&&+typeof+value.then+===+'function';
}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

I use this function as a universal solution:

<pre class="lang-js prettyprint-override"><code>function isPromise(value) {
 return value &amp;&amp; value.then &amp;&amp; typeof value.then === 'function';
}
</code></pre>

entityMap|blocks|key|65p2c|text|const+isPromise+=+(value)+=>+{
++return+!!(
++++value+&&
++++value.then+&&
++++typeof+value.then+===+'function'+&&
++++value?.constructor?.name+===+'Promise'
++)
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3s422|至于我--这张支票更好，试试吧|unstyled^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$C|D]]|$2|E|4|F|6|G|8|I|9|@]|A|@]|B|$]]]]

<pre><code>const isPromise = (value) =&gt; {
 return !!(
 value &amp;&amp;
 value.then &amp;&amp;
 typeof value.then === 'function' &amp;&amp;
 value?.constructor?.name === 'Promise'
 )
}
</code></pre>
As for me - this check is better, try it out

entityMap|blocks|key|d3p3o|text|ES6：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|31kgr|const+promise+=+new+Promise(resolve+=>+resolve('olá'));

console.log(promise.toString().includes('Promise'));+//true|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

ES6:

<pre><code>const promise = new Promise(resolve =&gt; resolve('olá'));

console.log(promise.toString().includes('Promise')); //true
</code></pre>

Whether it's an ES6 Promise or a bluebird Promise, Q Promise, etc.

How do I test to see if a given object is a Promise?

How do I tell if an object is a Promise?

 无论是ES6承诺，还是蓝鸟承诺，Q承诺，等等。 如何测试给定的对象是否为Promise？

问如何判断对象是否为Promise？
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