展開運算符 Spread Operator

「...」 後面必定是陣列

const params = [ "hi", 3 ,true ];
const other = [ 1, 2, ...params ];   //[1,2,"hi",3 true]

• 用在函式呼叫

  function sum(a,b,c){
  	return a + b + c
  }
  
  const args =[1,2,3];
  
  sum(...args)          
  
  //6
  

• 把可迭代(String/Array/TypedArray/Map/Set)或與陣列相似的物件轉成陣列

  const aString = "foo"
  const char = [...aString]
  
  //[ "f", "o","o" ]
  

• 將類陣列轉為陣列

  let doms = document.querySelectorAll('li')
  let newDoms = [...doms] //變成陣列了
  

其餘運算符 Other Operator

收集剩餘的值，並轉成陣列
位置必定在最後一位

function leftMoney(ming, ...money){
	console.log(ming, money)
}

leftMoney('小明', 100, 200, 300) //小明 [100, 200, 300]

• 將「不確定數量的傳入參數值」在函式中轉成陣列來運算

function sum(...numbers){
	const result = 0
	
	numbers.forEach(function (number)){
		result += number
	})
	return result
	} 
}

sum(1) //1
sum(1,2,3,4,5) //15

• 用在解構賦值

const [x, ...y] = [1, 2, 3]

console.log(x) //1
console.log(y) //[2,3]

const [x, y, ...z] = [1]

console.log(x) //1
console.log(y) //undefined
console.log(z) //[]

其餘參數的值在傳入的時候沒有實際值時，會是空陣列