text: const dogs = new Map();
  dogs.set('Snickers',3);
  dogs.set('sunny',2);
  dogs.set('Hugo',11);
  
  
  // dogs.forEach((key,val) => console.log(key, val));
  // 可以迭代的都可以使用for of
  for(const [key,val] of dogs) {
      console.log(key, val);
  }
  
  let a = 1;
  let b = 2;
  [a,b] = [b,a];
  console.log([a,b]);
  