Relationship Between Instance Objects and Constructors

Relationship Between Instance Objects and Constructors

1. Instance objects are created through constructors—the process of creation is called instantiation.
2. How to determine whether the object is of this data type?

• Instance object through constructor. Constructor == constructor name

//自定义构造函数
function Person(name,age) {
    
    
	this.name=name;
	this.age=age;
}
//实例化对象
var per=new Person("小明",15);
//通过构造器判断对象是不是属于Person的实例
console.dir(per.constructor===Person);//true

• Object instanceof constructor name

//自定义构造函数
		function Person(name,age) {
    
    
			this.name=name;
			this.age=age;
		}
		//实例化对象
		var per=new Person("小明",15);
		//通过instanceof判断对象是不是属于Person的实例
		console.dir(per instanceof Person);//true

3. Drawbacks of constructors

//自定义构造函数
		function Person(name,age) {
    
    
			this.name=name;
			this.age=age;
		}
		function Student(sex) {
    
    
			this.sex=sex;
		}
		//改变原型指向
		Student.prototype=new Person();
		//实例化对象
		var stu=new Student();
		//通过构造器判断stu的指向是不是Student
		console.dir(stu.constructor==Student);//false
		console.dir(stu instanceof Student);//true

Summarize:

Inheritance will change the pointer of the constructor, so it is not recommended to use the constructor constructor to judge whether the object is an instance of a constructor. It is recommended to use instanceof to judge