JS之理解对象

Posted 2020-08-05

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1.proto

每个对象都有一个proto属性，指向该对象的原型对象

<script>
        var person = function(name,city){
            this.name = name;
            this.city =city;   
        }
        person.prototype.showName = function(){
            return this.name;   
        }
        var p = new person(‘pmx‘,‘shanghai‘);
        console.log(p.__proto__ == person.prototype);
</script>

2.isPrototypeOf(obj)用来判断当前对象是否是obj的原型对象

<script>
      var person = function(name,city){
            this.name = name;
            this.city =city;   
        }
        person.prototype.showName = function(){
            return this.name;   
        }
        var p = new person(‘pmx‘,‘shanghai‘);
        console.log(person.prototype.isPrototypeOf(p));
</script>

3.getPrototypeOf(obj)得到obj的原型对象

<script>
      var person = function(name,city){
            this.name = name;
            this.city =city;   
        }
        person.prototype.showName = function(){
            return this.name;   
        }
        var p = new person(‘pmx‘,‘shanghai‘);
        console.log(Object.getPrototypeOf(p) == person.prototype);
</script>

4.hasOwnProperty用来判断属性是存在于本身还是原型对象中

<script>
      var person = function(name,city){
            this.name = name;
            this.city =city;   
        }
        person.prototype.age = 26;
        person.prototype.showName = function(){
            return this.name;   
        }
        var p = new person(‘pmx‘,‘shanghai‘);
        console.log(p.hasOwnProperty("name"));
        console.log(p.hasOwnProperty("age"));
</script>

5.in用来判断obj是否有指定属性，不论该属性存在于对象上，还是原型链上

<script>
      var person = function(name,city){
            this.name = name;
            this.city =city;   
        }
        person.prototype.age = 26;
        person.prototype.showName = function(){
            return this.name;   
        }
        var p = new person(‘pmx‘,‘shanghai‘);
        console.log("name" in p);
        console.log("age" in p);
</script>