js 基础（一）

let  p1 = {
  name: 'shangyy',
  age: 18,
}

function func(person) {
  person.age = 25;
  person= {
    name: 'huyating',
    age: 20,
  };
  return person;
}

const p2 = func(p1);
console.log(p1); // { name: 'shangyy', age: 25 }
console.log(p2); // { name: 'huyating', age: 20 }

 

function test(a){
  var a;
  console.log(a);
  function a(){
    console.log('a')
  }

}

test(1); // [Function: a]

 * 不会申明提前

* 暂时性死区

* 不会=挂载待window 上

var a = 123;
function test () {
  console.log(a); //a is not defined
  let a=1;
  
}

test (1);