栈内存空间数据复制示例
var a = `I am variable a`;
var b = a; 
console.log(b); //`I am variable a`
b = `I am variable b`;
console.log(a); //`I am variable a`
console.log(b); //`I am variable b`

var a = {
  name : `I am object a`,
  type : 'object'
}

var b = a;
console.log(b);
// {name: "I am object a", type: "object"}

b.name = `I am object b`;

console.log(a);
// {name: "I am object b", type: "object"}

console.log(b);

// {name: "I am object b", type: "object"}

变量a和变量b的引用不同，对象就不是同一个对象
var a = {name:'Jay'};
var b = {name:'Jay'};
a===b //false

var obj = {
  name: 'Jay Chou',
  age: 32,
  song:{
    name:'发如雪',
    year:2007
  }
}
var obj1 = obj;
function shallowCopy(obj){
  var scObj = {};
  for(var prop in obj){
    if(obj.hasOwnProperty(prop)){
      scObj[prop] = obj[prop]
    }
  }
  return scObj;
}
var obj2 = shallowCopy(obj);
console.log(obj === obj1,'obj === obj1','赋值');
console.log(obj === obj2,'obj === obj2','浅拷贝');
// true "obj === obj1" "赋值"
// false "obj === obj2" "浅拷贝"
console.log(obj.song === obj2.song);
//true
obj2.song.name='双截棍';
obj2.name='Jay';
console.log(obj)
// {name: "Jay Chou", age: 32, song: {name:'双截棍',year:2007}}
console.log(obj1);
// {name: "Jay Chou", age: 32, song: {name:'双截棍',year:2007}}
console.log(obj2);
{name: "Jay", age: 32, song: {name:'双截棍',year:2007}}
console.log(obj===obj1)
//true
console.log(obj===obj2)
//false

var obj = {
  name: 'Jay Chou',
  age: 32,
  song:{
    name:'发如雪',
    year:2007
  }
}

var dcObj=JSON.parse(JSON.stringify(obj));

console.log(dcObj);
// {name: "Jay Chou", age: 32, song: {name:'发如雪',year:2007}}
console.log(dcObj.song === obj.song);
//false
dcObj.name='Jay';
dcObj.song.name='双截棍';
console.log(obj);
// {name: "Jay Chou", age: 32, song: {name:'发如雪',year:2007}}
console.log(dcObj);
//{name: "Jay", age: 32, song: {name:'双截棍',year:2007}}