参数扩展

1.收集剩余参数到一个数组中

function show(a,...args){  //...args必须为最后一个形参
        console.log(a)
        console.log(args)
    }
    show(2,13,14)  //2 [13,14]

2.数组展开(...arr 表示把数组arr展开)

例1

let arr=[1,2,3]

    function show(a,b,c)
    {
        console.log(a,b,c)
    }

    show(...arr) //等价于show(1,2,3)

例2

let arr1=[1,2,3]

    let arr2=[5,6,7]

    let arr=[...arr1,...arr2]

    console.log(arr) //[1,2,3,5,6,7]

例3

function show(...args)
    {
        fn(...args)
    }

    function fn(a,b)
    {
        console.log(a+b)
    }
  
    show(3,4) //7

默认参数

function show(a,b=5,c=12)
    {
        console.log(a,b,c)
    }

    show(99) //99 5 12
    show(99,100,101) //99,100,101