扩展 Node.js 类时的花括号

问题描述

为什么我们在扩展 Node.js 类时将变量包裹在花括号中，例如 {EventEmitter} = require 'events'?

Why do we wrap our variables in curly braces, like {EventEmitter} = require 'events', when extending a Node.js class?

例如，Trevor Burnham 在他的教程中关于事件-Driven CoffeeScript，以这种方式扩展 Node 的 EventEmitter:

For example, Trevor Burnham, in his tutorial on Event-Driven CoffeeScript, extends Node's EventEmitter this way:

{EventEmitter} = require 'events'

class Rooster extends EventEmitter
  constructor: ->
    @on 'wake', -> console.log 'COCKADOODLEDOO!'

(foghorn = new Rooster).emit 'wake' # COCKADOODLEDOO!

推荐答案

这个:

{EventEmitter} = require 'events'

相当于这个JavaScript:

is equivalent to this JavaScript:

var EventEmitter;
EventEmitter = require('events').EventEmitter;

当您require 'events' 时，您将使用模块的导出返回一个对象，其中一个导出是EventEmitter类".使用 {EventEmitter} 只是将 EventEmitter 从 require 'events' 返回的对象中拉出的惯用快捷方式；你也可以这样说:

When you require 'events', you're getting an object back with the module's exports, one of those exports is the EventEmitter "class". Using {EventEmitter} is just an idiomatic shortcut for pulling EventEmitter out of the object that require 'events' returns; you could also say this:

EventEmitter = require('events').EventEmitter

如果您愿意.当您想要提取对象的多个部分时，支撑版本开始派上用场.例如，这个:

if you prefer. The braced version starts to come in handy when you want to extract more than one part of an object; for example, this:

{a, b} = c

就像这样的JavaScript:

is like this JavaScript:

var a, b;
a = c.a;
b = c.b;

CoffeeScript 文档的 解构赋值 部分现在可能会成为一些不错的读物.

The Destructuring Assignment section of the CoffeeScript documentation might make some good reading right about now.

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