javascript - CoffeeScript 作业

Question

我对此代码有疑问:

getContent: (index) ->
  content = @get('content')
  element = content.objectAt(index)
  if element?
    [type, clientId] = element
    store = @get('store')

    if clientId?
      store.findByClientId(type, clientId)

我专门谈论这一行:

[type, clientId] = element

我不明白如何从一个变量分配两个值。

元素必须是数组才能使上面的内容成功地将值分配给左侧数组吗？

Answer 1

I do not understand how I can assign two values from one variable.

CoffeeScript 实现了它所谓的 Destructuring Assignment 。完整说明见http://coffeescript.org/#destructuring ，但我从中提取了一些示例以在此处展示。

它可以用于简单的列表分配。

weatherReport = (location) ->
  # Make an Ajax request to fetch the weather...
  [location, 72, "Mostly Sunny"]

[city, temp, forecast] = weatherReport "Berkeley, CA"

解构赋值语句编译到的位置

_ref = weatherReport("Berkeley, CA"), city = _ref[0], 
temp = _ref[1], forecast = _ref[2];

Would element have to be an array in order for the above to successfully assign values to the left hand side array?

不，它也可以用于对象。来自 CoffeeScript 文档“解构赋值可以与任何深度的数组和对象嵌套一起使用，以帮助提取深度嵌套的属性。”

futurists =
  sculptor: "Umberto Boccioni"
  painter:  "Vladimir Burliuk"
  poet:
    name:   "F.T. Marinetti"
    address: [
      "Via Roma 42R"
      "Bellagio, Italy 22021"
    ]

{poet: {name, address: [street, city]}} = futurists

解构赋值语句编译到的位置

_ref = futurists.poet, 
name = _ref.name, (_ref1 = _ref.address, street = _ref1[0], city = _ref1[1]);