let func = (x = 1, y = 2) => {
    console.log(x ,y)
}
func()
// 1, 2

let func2 = ({x=0, y=0}={}) => {
    console.log(x, y)
}
func2()
// 0, 0
func2({x:1, y:2})
// 1, 2

let func = (x=1, y=2) => {
    let x = 2  // 錯誤
    console.log(x ,y)
}
func()
// Uncaught SyntaxError: Identifier 'x' has already been declared
 

let func = (...a) => {
    console.log(a)
}
func(1,2,3,4,5)
// [1,2,3,4,5]


let func = (a,b,c) => {
    console.log(a,b,c)
}
func(...[1,2,3])
// 1,2,3


// 剩餘運算子 必須在最後一個引數
let func = (a,b,...c) => {
    console.log(a,b,c)
}
func(1,2,3,4,5)
// 1,2,[3,4,5]