Question

我正在试图找出下面代码中发生的事情，该代码涉及将一个对象复制到另一个对象上。在某些情况下，它们的行为与改变另一个改变另一个的同一个对象相同。我发现了许多关于如何通过引用复制javascript对象的帖子，因此它们实际上是同一个对象。例如，来自http://www.w3schools.com/js/js_object_definition.asp：

 var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"} 
 var x = person;  // This will not create a copy of person. 
 x.age = 10; // This will change both x.age and person.age

 The object x is not a copy of person. It is person. Both x and person
 is the same object. Any changes to x will also change person, because
 x and person are the same object.

但是，我还发现了一个对象看起来像是单独对象的情况。它如何在一种情况下像同一个对象一样，但在另一种情况下却不同？我很感激有关情况的任何启示：

示例：http://codepen.io/gratiafide/pen/yagQGr?editors=1010#0

HTML：

<div id="app">
  <my-component>
  </my-component>
</div>

JS：

  var MyComponent = Vue.extend({
  template: '<div v-on:click="test()" class="red">1.  Click here to copy the name object to message and change the value of name to see if the value of message gets changed also.  (It does not).</div>  message: {{ message | json}} <br> name: {{ name | json}}<div v-on:click="test2()" class="red">2.  Now click here to see if updating  the name object also changes the message object.  It does!  Why here and not in #1?</div><div v-on:click="test3()" class="red">3.  Click here to see yet another way of updating the name object also changes the message object. Why here and not in #1?</div>',

  data: function () {
    return { 
    message: {},
    name: {}
    }
  },

  ready: function(){
    this.message = {};
  },
  methods: {
    test: function(){
       this.message = {'t1':"m1"};
       this.name = this.message;  
       this.name = {'t2':"m2"};  
    },
    test2: function(){
       this.message = {'t1':"m1"};
       this.name = this.message;  
       for (var key in this.name) {
                this.name[key] = '';
            }  
    },
    test3: function(){
       this.message = {'t1':"m1"};
       this.name = this.message;  
       Vue.set(this.name, 't1', 'm2');
    }
  }
});

Vue.component('my-component', MyComponent);

new Vue({
  el: '#app'
});

CSS：

@import url(https://fonts.googleapis.com/css?family=Open+Sans);

.red{
  color:red;  
}

body {
  font-family: 'Open Sans', sans-serif;
  background: rgba(0,0,0,.5);
  margin: 0;
}

#app {
  width: 500px;
  margin: 0 auto;
  padding: 10px 20px;
  background: rgba(255,255,255,.9);
}

Answer 1

基本上，你要问的是这三者之间的区别：

this.message = {'t1':"m1"};
this.name = this.message;  

#1:
this.name = {'t2':"m2"};  

#2
for (var key in this.name) {
  this.name[key] = '';
}  

#3
Vue.set(this.name, 't1', 'm2');

在第一种情况下，您不会更改this.message，因为您要将全新对象分配给this.name。这个新对象（{'t2':"m2"}）与this.message完全无关。

也许您正在尝试/想做的事情是：

this.name.t2 = "m2";

与＃2和＃3相同，影响this.message，因为this.name 仍然指的是同一个对象。

要将新属性从另一个对象分配到现有对象，您可以在支持此功能的浏览器中使用Object.assign：

Object.assign(this.name, {'t2':"m2"});

Answer 2

有两种类型的变量，值和参考。所有基元（即字符串，数字和布尔值）都按值存储，其他所有基元都通过引用存储，并且可以具有属性。

＆＃13;

var a,b;
a={c:1};
b=a;
console.log (b===a); // true;

b={c:1}; // note that b is now being assigned a new reference.
console.log (b===a); // false;

a=b; // now a is being assigned the reference of b.
console.log (b===a); // true;

a.c=2; //note that it is the property of a (c) got changed, not a itself.
console.log (b===a); // true;

a.a = a; //now a has a property (a) that stores the reference of a.
console.log(a === a.a);
console.log(a.a === a.a.a);
console.log(a.a === a.a.a.a.a.a.a.a.a);
a.a.a.a.a.a.a.a.a.a.a.c = 10;
console.log(a.c)//10;

＆＃13;

＆＃13; 声明变量有不同的方法，但这不是问题的范围。

一个案例中的同一个对象，另一个案例中的不同对

2 个答案: