CoffeeScript 解构赋值

CoffeeScript 实现 ECMAScript Harmony 的提议 解构赋值 语法, 这样从复杂的数组和对象展开数据会更方便一些. 当你把数组或者对象的字面量赋值到一个变量时, CoffeeScript 把等式两边都解开配对, 把右边的值赋值给左边的变量. 最简单的例子, 可以用来并行赋值:

theBait   = 1000
theSwitch = 0
 
[theBait, theSwitch] = [theSwitch, theBait]

var theBait, theSwitch, _ref;
 
theBait = 1000;
 
theSwitch = 0;
 
_ref = [theSwitch, theBait], theBait = _ref[0], theSwitch = _ref[1];

用来处理函数多返回值也很方便。

weatherReport = (location) ->
  # 发起一个 Ajax 请求获取天气...
  [location, 72, "Mostly Sunny"]
 
[city, temp, forecast] = weatherReport "Berkeley, CA"

var city, forecast, temp, weatherReport, _ref;
 
weatherReport = function(location) {
  return [location, 72, "Mostly Sunny"];
};
 
_ref = weatherReport("Berkeley, CA"), city = _ref[0], temp = _ref[1], forecast = _ref[2];

解构赋值可以用在深度嵌套的数组跟对象上, 取出深度嵌套的属性。

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

var city, futurists, name, street, _ref, _ref1;
 
futurists = {
  sculptor: "Umberto Boccioni",
  painter: "Vladimir Burliuk",
  poet: {
    name: "F.T. Marinetti",
    address: ["Via Roma 42R", "Bellagio, Italy 22021"]
  }
};
 
_ref = futurists.poet, name = _ref.name, (_ref1 = _ref.address, street = _ref1[0], city = _ref1[1]);

解构赋值还可以跟 splats 搭配使用。

tag = ""
[open, contents..., close] = tag.split("")

var close, contents, open, tag, _i, _ref,
  __slice = [].slice;
 
tag = "";
_ref = tag.split(""), open = _ref[0], contents = 3 <= _ref.length ? __slice.call(_ref, 1, _i = _ref.length - 1) : (_i = 1, []), close = _ref[_i++];

展开式(expansion)可以用于获取数组结尾的元素, 而不需要对中间过程的数据进行赋值. 它也可以用在函数参数的列表上。

text = "Every literary critic believes he will
        outwit history and have the last word"
 
[first, ..., last] = text.split " "

var first, last, text, _ref;
 
text = "Every literary critic believes he will outwit history and have the last word";
 
_ref = text.split(" "), first = _ref[0], last = _ref[_ref.length - 1];

解构赋值也可以用在 class 的构造器上, 从构造器配置对象赋值到示例属性上。

class Person
  constructor: (options) -> 
    {@name, @age, @height} = options
 
tim = new Person age: 4

var Person, tim;
 
Person = (function() {
  function Person(options) {
    this.name = options.name, this.age = options.age, this.height = options.height;
  }
 
  return Person;
 
})();
 
tim = new Person({
  age: 4
});

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