es6进口副作用意义 [英] es6 import for side effects meaning

问题描述

我正在阅读es6导入语句 MDN参考。语法：

I was reading the es6 import statement reference on MDN. The syntax:

import "my-module";

仅导入整个模块的副作用，而不导入任何绑定。我不确定副作用是什么意思。我用角度使用 importangular。 Angular绑定到窗口但不返回对象。所以我不知道这是否会被完全称为副作用。

will import an entire module for side effects only, without importing any bindings. I am not sure what side effects mean. I have been using with angular by saying import "angular". Angular binds to window but does not return a object. So I am not sure if this would be called as a side effect exactly.

推荐答案

当你需要导入没有' t导出任何东西，但做其他事情，这是一个副作用只有模块。

When you need to import something that doesn't export anything, but does something else, this is a side effect only module. You import it only to initialize it.

纯纯模块

如果您将模块视为函数，则仅通过导出其内容来影响作用域的模块就像一个总是返回相同内容的函数（没有参数的纯函数）。无论多少次导入反应15.01，您将始终获得一个包含相同方法的对象。

If you think about modules as functions, a module that only effects the scope by exporting it's content is like a function that always returns the same thing (a pure function without parameters). No matter how many times you'll import react 15.01, you'll always get an object that contains the same methods.

具有副作用的模块是一个更改的模块范围在其他方面然后返回一些东西，它的效果并不总是可预测的，并且可以受到外力（非纯功能）的影响。例如，一个polyfill可能不会做任何事情，因为它发现它启用的功能已被浏览器支持。

A module with side-effects is one that changes the scope in other ways then returning something, and it's effects are not always predictable, and can be affected by outside forces (non pure function). A polyfill for example, might not do anything, because it finds that the feature that it enables is already supported by the browser.

副作用示例： / strong>

Examples of side effects:

• Angular绑定到全局窗口对象，但不导出
  任何东西。


• 在不支持
  的浏览器中启用ES6功能的polyfill可以支持它们，如 babel polyfill 是一个副作用。


• 许多jQuery插件将自己附加到全局jQuery对象。 / li>
  
• 在后台运行的分析模块，监控用户交互，并将数据发送到服务器。


• 在webpack中导入CSS可以认为是如果您不使用CSS模块，则会生效。

• Angular binds to the global window object, but doesn't export anything.
• A polyfill that enables ES6 features in the browsers that don't support them, like babel polyfill is a side effect.
• Many jQuery plugins attach themselves to the global jQuery object.
• Analytics modules that run in the background, monitor user interaction, and send the data to a server.
• Importing CSS in webpack can be considered a side effect if you're not using CSS modules.

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