带块的常量声明 [英] Constant declaration with block

问题描述

最近我正在研究Firefox Add-on Builder SDK源代码，以及偶然发现了这样的常量声明：

Recently I was looking into Firefox Add-on Builder SDK sources, and stumbled on such constants declaration:

const { getCodeForKey, toJSON } = require("../../keyboard/utils");

我可以找到有关 CommonJS模块，但是这项任务的左侧部分让我感到困惑，因为它必须是特定于语言的，而且我无法谷歌上的任何内容。

I could find information about CommonJS Modules, but left part of this assignment slightly confuses me, since it must be language specific, and I couldn't google anything on that.

有人可以指点我的一些规格/草案来解释这里发生了什么吗？

Can someone point me to some specification/draft that explains what's going on here?

推荐答案

这是一个解构分配，目前只有Firefox使用的SpiderMonkey JavaScript引擎。以下是它如何与数组一起使用：

This is a destructuring assignment, something that is currently only implemented by the SpiderMonkey JavaScript engine which is used by Firefox. Here is how it works with arrays:

// Destructuring assignment
[a, b] = foo;

// Equivalent code
a = foo[0];
b = foo[1];

以下是对象的工作原理：

And here is how it works with objects:

// Destructuring assignment
{a, b} = foo;

// Equivalent code
a = foo.a;
b = foo.b;

稍微复杂的例子：

// Destructuring assignment
{name: a, address: {line1: b}} = foo;

// Equivalent code
a = foo.name;
b = foo.address.line1;

所以你的代码示例相当于：

So your code example is equivalent to:

var utilsExports = require("../../keyboard/utils");
const getCodeForKey = utilsExports.getCodeForKey;
const toJSON = utilsExports.toJSON;

这只是一种更方便的写作方式。

It is merely a more convenient way to write it.

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