ES6---函数

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

show("welcome","牧马人");

设置默认参数写法

function show(a="welcome",b="牧马人"){


}

function(x,y){
let x="1";
let y="2";
}

会报错，，已经重复定义了x，y

let arr=["apple","banana","orange"];

  console.log(arr);  结果:["apple","banana","orange"]
  console.log(...arr) ;结果: apple banana orange

function(...a){
   console.log(a)
}

show("a","b","c","d")

结果是["a","b","c","d"]

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

function(...[1,2,3])

function show(){
 return 1;
}

改写成
let show=（）=>1
()=> return的东西
()=> {
    语句
    return;
  }

show=(a,b)=>{
   console.log(a,b)
   return a+b;
}