blocks|key|4424456|text|看起来答案是，到目前为止，你不能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424457|http://exploringjs.com/es6/ch_modules.html#sec_module-loader-api|offset|length|4424458|我认为这样做的目的是尽可能多地启用静态分析，而有条件的导入模块则打破了这一点。另外值得一提的是--我使用的是Babel，我猜System不受Babel支持，因为模块加载器API没有成为ES6标准。|style|CODE|4424459|entityMap|0|LINK|mutability|MUTABLE|url|1|https://babeljs.io/^0|0|0|1S|0|0|1Q|6|1I|5|1|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@$D|U|E|V|1|W]]|A|$]]|$1|F|3|G|5|6|7|X|8|@$D|Y|E|Z|H|I]]|9|@$D|10|E|11|1|12]]|A|$]]|$1|J|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|C]]|Q|$5|M|N|O|A|$P|R]]]]

Looks like the answer is that, as of now, you can't.

<a href="http://exploringjs.com/es6/ch_modules.html#sec_module-loader-api" rel="noreferrer">http://exploringjs.com/es6/ch_modules.html#sec_module-loader-api</a>

I think the intent is to enable static analysis as much as possible, and conditionally imported modules break that. Also worth mentioning -- I'm using <a href="https://babeljs.io/" rel="noreferrer">Babel</a>, and I'm guessing that <code>System</code> is not supported by Babel because the module loader API didn't become an ES6 standard.

blocks|key|4424384|text|如果你愿意，你可以使用require。这是一种使用条件要求语句的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424385|let+something+=+null;
let+other+=+null;

if+(condition)+{
++++something+=+require('something');
++++other+=+require('something').other;
}
if+(something+&&+other)+{
++++something.doStuff();
++++other.doOtherStuff();
}|code-block|syntax|javascript|4424386|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you'd like, you could use require. This is a way to have a conditional require statement.

<pre><code>let something = null;
let other = null;

if (condition) {
 something = require('something');
 other = require('something').other;
}
if (something &amp;&amp; other) {
 something.doStuff();
 other.doOtherStuff();
}
</code></pre>

blocks|key|4424435|text|您不能有条件地导入，但您可以做相反的事情:有条件地导出某些内容。这取决于您的用例，因此这项工作可能不适合您。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424436|您可以执行以下操作：|4424437|api.js|4424438|import+mockAPI+from+'./mockAPI'
import+realAPI+from+'./realAPI'

const+exportedAPI+=+shouldUseMock+?+mockAPI+:+realAPI
export+default+exportedAPI|code-block|syntax|javascript|4424439|apiConsumer.js|4424440|import+API+from+'./api'
...|4424441|我用它来模拟像mixpanel这样的分析库。因为我现在不能有多个版本或者我们的前端。不是最优雅的，但很管用。根据环境的不同，我只在这里和那里设置了一些“if”，因为在mixpanel中，它需要初始化。|4424442|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|V|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You can't import conditionally, but you can do the opposite: export something conditionally. It depends on your use case, so this work around might not be for you.

You can do:

api.js

<pre><code>import mockAPI from './mockAPI'
import realAPI from './realAPI'

const exportedAPI = shouldUseMock ? mockAPI : realAPI
export default exportedAPI
</code></pre>

apiConsumer.js

<pre><code>import API from './api'
...
</code></pre>

I use that to mock analytics libs like mixpanel, etc... because I can't have multiple builds or our frontend currently. Not the most elegant, but works. I just have a few 'if' here and there depending on the environment because in the case of mixpanel, it needs initialization.

blocks|key|4424475|text|我们现在有动态进口提案与ECMA。这是第3阶段。这也可以作为babel-preset使用。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4424476|下面是根据你的情况进行条件渲染的方法。|4424477|if+(condition)+{
++++import('something')
++++.then((something)+=>+{
+++++++console.log(something.something);
++++});
}|code-block|syntax|javascript|4424478|这基本上返回了一个承诺。promise的解决方案预计会有该模块。该提议还具有其他功能，如多个动态导入，默认导入，js文件导入等。你可以找到更多关于dynamic+imports+here的信息。|4424479|entityMap|0|LINK|mutability|MUTABLE|url|https://babeljs.io/docs/plugins/syntax-dynamic-import/|1|http://2ality.com/2017/01/import-operator.html^0|U|C|0|0|0|0|21|K|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

We do have dynamic imports proposal now with ECMA. This is in stage 3. This is also available as <a href="https://babeljs.io/docs/plugins/syntax-dynamic-import/" rel="noreferrer">babel-preset</a>.

Following is way to do conditional rendering as per your case.

<pre><code>if (condition) {
 import('something')
 .then((something) =&gt; {
 console.log(something.something);
 });
}
</code></pre>

This basically returns a promise. Resolution of promise is expected to have the module. The proposal also have other features like multiple dynamic imports, default imports, js file import etc. You can find more information about <a href="http://2ality.com/2017/01/import-operator.html" rel="noreferrer">dynamic imports here</a>.

blocks|key|4424514|text|在评估中隐藏它对我来说很有效，对静态分析器隐藏它...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424515|if+(typeof+__CLI__+!==+'undefined')+{
++eval("require('fs');")
}|code-block|syntax|javascript|4424516|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

obscuring it in an eval worked for me, hiding it from the static analyzer ...

<pre><code>if (typeof __CLI__ !== 'undefined') {
 eval("require('fs');")
}
</code></pre>

blocks|key|4424629|text|require()是一种在运行时导入某些模块的方法，如果与字符串文本路径一起使用，它同样有资格进行像import这样的静态分析。这是bundler为捆绑包挑选依赖项所必需的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4424630|const+defaultOne+=+require('path/to/component').default;
const+NamedOne+=+require('path/to/component').theName;|code-block|syntax|javascript|4424631|对于具有完整静态分析支持的动态模块解析，首先在索引器(index.js)中索引模块，然后在主机模块中导入索引器。|4424632|//+index.js
export+{+default+as+ModuleOne+}+from+'path/to/module/one';
export+{+default+as+ModuleTwo+}+from+'path/to/module/two';
export+{+SomeNamedModule+}+from+'path/to/named/module';

//+host.js
import+*+as+indexer+from+'index';
const+moduleName+=+'ModuleOne';
const+Module+=+require(indexer[moduleName]);|4424633|entityMap^0|0|9|1E|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

<code>require()</code> is a way to import some module on the run time and it equally qualifies for static analysis like <code>import</code> if used with string literal paths. This is required by bundler to pick dependencies for the bundle.

<pre><code>const defaultOne = require('path/to/component').default;
const NamedOne = require('path/to/component').theName;
</code></pre>

For dynamic module resolution with complete static analysis support, first index modules in an indexer(index.js) and import indexer in host module.

<pre><code>// index.js
export { default as ModuleOne } from 'path/to/module/one';
export { default as ModuleTwo } from 'path/to/module/two';
export { SomeNamedModule } from 'path/to/named/module';

// host.js
import * as indexer from 'index';
const moduleName = 'ModuleOne';
const Module = require(indexer[moduleName]);
</code></pre>

blocks|key|4424616|text|我能够使用一个立即调用的函数和require语句来实现这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424617|const+something+=+(()+=>+(
++condition+?+require('something')+:+null
))();

if(something)+{
++something.doStuff();
}|code-block|syntax|javascript|4424618|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I was able to achieve this using an immediately-invoked function and require statement.

<pre><code>const something = (() =&gt; (
 condition ? require('something') : null
))();

if(something) {
 something.doStuff();
}
</code></pre>

blocks|key|4424624|text|条件导入也可以通过三元和require()实现：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4424625|const+logger+=+DEBUG+?+require('dev-logger')+:+require('logger');|4424626|此示例取自ES+Lint+global-require文档：https://eslint.org/docs/rules/global-require|4424627|entityMap|0|LINK|mutability|MUTABLE|url|https://eslint.org/docs/rules/global-require^0|C|9|0|0|1T|0|U|18|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@]|D|@$9|Y|A|Z|1|10]]|E|$]]|$1|J|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]]]

Conditional imports could also be achieved with a ternary and <code>require()</code>s:

<code>const logger = DEBUG ? require('dev-logger') : require('logger');</code>

This example was taken from the ES Lint global-require docs: <a href="https://eslint.org/docs/rules/global-require" rel="nofollow noreferrer">https://eslint.org/docs/rules/global-require</a>

blocks|key|4424675|text|使用动态导入Webpack模式eager时的重要区别|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4424676|if+(normalCondition)+{
++//+this+will+be+included+to+bundle,+whether+you+use+it+or+not
++import(...);
}

if+(process.env.SOMETHING+===+'true')+{
++//+this+will+not+be+included+to+bundle,+if+SOMETHING+is+not+'true'
++import(...);
}|code-block|syntax|javascript|4424677|entityMap^0|F|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Important difference if you use dynamic import Webpack mode <code>eager</code>:

<pre class="lang-js prettyprint-override"><code>if (normalCondition) {
 // this will be included to bundle, whether you use it or not
 import(...);
}

if (process.env.SOMETHING === 'true') {
 // this will not be included to bundle, if SOMETHING is not 'true'
 import(...);
}
</code></pre>

blocks|key|4424816|text|2020年更新|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424817|现在，您可以将import关键字作为函数(即import())调用，以便在运行时加载模块。|offset|length|style|CODE|4424818|示例：|4424819|const+mymodule+=+await+import(modulename);|code-block|syntax|javascript|4424820|或者：|4424821|import(modulename)
++++.then(mymodule+=>+/*+...+*/);|4424822|请参阅https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#Dynamic_Imports|4424823|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#Dynamic_Imports^0|0|7|6|M|8|0|0|0|0|0|3|2R|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@$D|14|E|15|F|G]|$D|16|E|17|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|18|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|19|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|1B|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|1C|8|@]|9|@$D|1D|E|1E|1|1F]]|A|$]]|$1|U|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

<h1>2020 Update</h1>
You can now call the <code>import</code> keyword as a function (i.e. <code>import()</code>) to load a module at runtime.
Example:
<pre class="lang-js prettyprint-override"><code>const mymodule = await import(modulename);
</code></pre>
or:
<pre class="lang-js prettyprint-override"><code>import(modulename)
 .then(mymodule =&gt; /* ... */);
</code></pre>
See <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#Dynamic_Imports" rel="noreferrer">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#Dynamic_Imports</a>

blocks|key|4424846|text|JS中有条件的导入导出|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424847|const+value+=+(
++++await+import(`${condtion+?+`./file1.js`+:+`./file2.js`}`)
).default

export+default+value|code-block|syntax|javascript|4424848|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<h1> Import and Export Conditionally in JS </h1>
<pre><code>const value = (
 await import(`${condtion ? `./file1.js` : `./file2.js`}`)
).default

export default value
</code></pre>

blocks|key|4424774|text|用户可以通过以下链接了解有关动态导入的更多信息|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4424775|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#dynamic_imports|offset|length|4424776|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|2R|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

One can go through the below link to learn more about dynamic imports
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#dynamic_imports" rel="nofollow noreferrer">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#dynamic_imports</a>

I need to do something like:

<pre><code>if (condition) {
 import something from 'something';
}
// ...
if (something) {
 something.doStuff();
}
</code></pre>

The above code does not compile; it throws <code>SyntaxError: ... 'import' and 'export' may only appear at the top level</code>.

I tried using <code>System.import</code> as shown <a href="http://www.2ality.com/2013/07/es6-modules.html#module-loader-api" rel="noreferrer">here</a>, but I don't know where <code>System</code> comes from. Is it an ES6 proposal that didn't end up being accepted? The link to "programmatic API" from that article dumps me to a <a href="http://wiki.ecmascript.org/doku.php?id=harmony:module_loaders" rel="noreferrer">deprecated docs page</a>.

How can I conditionally import an ES6 module?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

教程

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云智能顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

聚焦“写作效率、视觉美观与运行性能”三方面进行全面升级，为您提供更高效、稳定的创作环境

社区富文本&Markdown编辑器全新改版上线，欢迎大家体验!

诚挚邀请您参与本次调研，分享您的真实使用感受与建议。您的反馈至关重要，感谢您的支持与参与！

社区新版编辑器体验调研

我需要做一些类似的事情：if (condition) {    import something from 'something';}// ...if (something) {    something.doStuff();}上面的代码没有编译；它抛出了SyntaxError: ... 'import' and 'e...

问如何有条件地导入ES6模块？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何有条件地导入ES6模块？EN