function.md

函数

箭头函数

1. 有且仅有1个参数，()可以省
2. 如果函数体只有一句话，而且是return，{}可以省
3. this 相当于回调外层的this

let add = (a,b)=>{
    return a+b;
}
console.log(add(2,3)) //5

let add1 = (a,b)=>a+b
console.log(add1(2,3)) //5

let add2 = a=>a+2
console.log(add2(2)) // 4

var obj = {name:'yk'}
function foo(){
  var id = 2
  var that = this
  console.log(that.name)  //yk
  setTimeout(() => {
    console.log(this===that)  //true
    console.log(this.name)  //yk
  }, 100);
}

foo.call(obj);  //true

默认参数

let add3 = (a=1,b=2,c=3)=>a+b+c
console.log(add3()) //6
console.log(add3(2,3)) //8

function fn({title='a'}={title:'b'}){
	console.log(title)
}

fn()
b

fn(1)
a

fn({name:'11'})
a

fn({})
a

参数展开

function(a,b,...名字) 名字自定义 剩余参数必须在参数列表的最后

let add4 = (a,b,...args)=>{
    console.log(a,b,args)
    return Math.max(...args)
}
add4(1,2,3,4,5,5,6,8)
// 1 2 [ 3, 4, 5, 5, 6, 8 ]

let add5 = (a,b,...args,c)=>{
    console.log(a,b,args,c)
} //Rest parameter must be last formal parameter
add4(1,2,3,4,5,5,6,8,111)

let sort = (a,b,...args)=>{
  console.log(args.sort())
}

add4(1,2,4,2)  //2,4

用途

• 接收剩余参数
• 展开数组

let arr = [1,2,3]
let arr2 = [1,2,...arr,3]
console.log(arr2) //[ 1, 2, 1, 2, 3, 3 ]

function show1(...args){
    show2(...args)
}
function show2(a,b){
    console.log(a,b)
}
show1(1,2) //1,2