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
  1. let add = (a,b)=>{
  2.     return a+b;
  3. }
  4. console.log(add(2,3)) //5
  6. let add1 = (a,b)=>a+b
  7. console.log(add1(2,3)) //5
  9. let add2 = a=>a+2
  10. console.log(add2(2)) // 4
  12. var obj = {name:'yk'}
  13. function foo(){
  14.   var id = 2
  15.   var that = this
  16.   console.log(that.name)  //yk
  17.   setTimeout(() => {
  18.     console.log(this===that)  //true
  19.     console.log(this.name)  //yk
  20.   }, 100);
  21. }
  23. foo.call(obj);  //true

默认参数

  1. let add3 = (a=1,b=2,c=3)=>a+b+c
  2. console.log(add3()) //6
  3. console.log(add3(2,3)) //8
  1. function fn({title='a'}={title:'b'}){
  2.     console.log(title)
  3. }
  5. fn()
  6. b
  8. fn(1)
  9. a
  11. fn({name:'11'})
  12. a
  14. fn({})
  15. 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

  1. let add4 = (a,b,...args)=>{
  2.     console.log(a,b,args)
  3.     return Math.max(...args)
  4. }
  5. add4(1,2,3,4,5,5,6,8)
  6. // 1 2 [ 3, 4, 5, 5, 6, 8 ]
  8. let add5 = (a,b,...args,c)=>{
  9.     console.log(a,b,args,c)
  10. } //Rest parameter must be last formal parameter
  11. add4(1,2,3,4,5,5,6,8,111)
  13. let sort = (a,b,...args)=>{
  14.   console.log(args.sort())
  15. }
  17. add4(1,2,4,2)  //2,4

用途

  • 接收剩余参数
  • 展开数组
  1. let arr = [1,2,3]
  2. let arr2 = [1,2,...arr,3]
  3. console.log(arr2) //[ 1, 2, 1, 2, 3, 3 ]
  5. function show1(...args){
  6.     show2(...args)
  7. }
  8. function show2(a,b){
  9.     console.log(a,b)
  10. }
  11. show1(1,2) //1,2