react学习三

      三点运算符  (...)的用法

     1：展开运算符

  let  a=[1,2,3];
  let  b=[0,...a,4];//[0,1,2,3,4]

  let  obj   ={a:1,b:2};
  let  obj2 ={...obj,c:3}; //{a:1,b:2,c:3};
  let  obj3 ={...obj,a:3};//{a:3,b:2}

　　2：剩余操作符，把剩余的东西放到一个array里面赋值给它

  let  a=[1,2,3];
  let [b,...c]=a;  //b  --1,c --[2,3]
  
  let a=[1,2,3];
  let [b,...[c,d,e]]=a;
  
  b; // 1
  c; // 2
  d; // 3
  e; // undefined

  function test(a,...rest){
  console.log(a);//1
  console.log(rest);//[2,3]
  }
   
   test(1,2,3)
 

   let array =[1,2,3,4,5];
   const {x,y,...z}=array;
   //其中z=[3,4,5],注意如果由于array的length不足以完成析构，则z为【】
   对象
   let obj={name:'zhangsan',age:30,city:'shenzhen'};
   const {name,...others}=obj;
   console.log(name);//'zhangsan'
   console.log(others);//{age:30,city:'shenzhen'}