我相信很多人都已經很熟悉 ES6 解構賦值。你知道也可以用在函式的參數裡嗎？

var sayHello = function({ name, surname }) {
  console.log(`Hello ${name} ${surname}! How are you?`);
};

sayHello({ name: 'John', surname: 'Smith' })
// -> Hello John Smith! How are you?

對函式來說可以接受一個可選擇的物件是非常有用的。對於這個使用方法，你可以加入預設參數來使用，不管是 caller 忘記賦值，或者是 caller 根本忘記傳送參數：

var sayHello2 = function({ name = "Anony", surname = "Moose" } = {}) {
  console.log(`Hello ${name} ${surname}! How are you?`);
};

= {} 意思說預設物件可以被解構成這個 {} 參數，萬一 caller 忘記傳送參數，或傳送一個錯誤的類型（更多關於在下面）。

sayHello2()
// -> Hello Anony Moose! How are you?
sayHello2({ name: "Bull" })
// -> Hello Bull Moose! How are you?
參數處理

使用解構賦值，如果輸入參數不符合函式指定的物件參數，所有不符合的參數都是 undefined，所以你需要加入程式碼來正確的處理這些不符合的參數：

var sayHelloTimes = function({ name, surname }, times) {
  console.log(`Hello ${name} ${surname}! I've seen you ${times} times before.`);
}

sayHelloTimes({ name: "Pam" }, 5678)
// -> Hello Pam undefined! I've seen you 5678 times before.
sayHelloTimes(5678)
// -> Hello undefined undefined! I've seen you undefined times before.

假設參數被解構時不存在的話，會拋出例外，可能會造成你的應用程式停止：

sayHelloTimes()
// -> Uncaught TypeError: Cannot match against 'undefined' or 'null'...

它的概念上類似於存取未定義對象的屬性，只是用不同的例外類型。

解構賦值某些程度上會隱藏所有預設參數：

var sayHelloTimes2 = function({ name = "Anony", surname = "Moose" } = {}, times) {
  console.log(`Hello ${name} ${surname}! I've seen you ${times} times before.`);
};

sayHelloTimes2({ name: "Pam" }, 5678)
// -> Hello Pam Moose! I've seen you 5678 times before.
sayHelloTimes2(5678)
// -> Hello Anony Moose! I've seen you undefined times before.
sayHelloTimes2()
// -> Hello Anony Moose! I've seen you undefined times before.

= {} 掩蓋了 object 屬性不存在的情況；但對於個別屬性預設值的情形下則是會拋出例外：

var sayHelloTimes2a = function({ name = "Anony", surname = "Moose" }, times) {
  console.log(`Hello ${name} ${surname}! I've seen you ${times} times before.`);
};

sayHelloTimes2a({ name: "Pam" }, 5678)
// -> Hello Pam Moose! I've seen you 5678 times before.
sayHelloTimes2a(5678)
// -> Hello Anony Moose! I've seen you undefined times before.
sayHelloTimes2a()
// -> Uncaught TypeError: Cannot match against 'undefined' or 'null'.
可用性

請注意解構賦值現在 Node.js 還有其他瀏覽器還無法使用。如果你想要試試看的話，你可以在 Node.js 使用 --harmony-destructuring。