参数默认值 (函数形参与对象数组解构)

• ES6 允许给函数参数，对象数组解构，赋值默认值。

应用场景

1. 形参初始值 具有默认值的参数。

   let add = (a, b, c = 10)=> {
       return a + b + c;
   }
   function add(a, b, c = 10) {
       return a + b + c;
   }
   

2. 与解构赋值结合

   let test = ({host="127.0.0.1", username, password, port})=> {
       console.log(host)
       console.log(username)
       console.log(password)
       console.log(port)
   }
   function test({host="127.0.0.1", username, password, port}) {
       console.log(host)
       console.log(username)
       console.log(password)
       console.log(port)
   }
   test({
       host: 'localhost',
       username: 'admin',
       password: 'root',
       port: 3306
   })