instanceof
- instanceof用于判断 "对象" 是否是指定构造函数的 "实例"
class Person{
constructor(myName) {
this.name = myName;
}
}
let p = new Person();
console.log(p instanceof Person); // true
class Cat{
name = "mm";
}
let mm = new Cat();
console.log(mm instanceof Person); // false
- instanceof 注意点
只要 构造函数的原型对象出现在实例对象的原型链中都会返回true
function Person(myName) {
this.name = myName;
}
function Student(myName, myScore){
Person.call(this,myName);
this.score = myScore;
}
Student.prototype = new Person();
Student.prototype.constructor = Student;
let stu = new Student();
console.log(stu instanceof Person); // true
isPrototypeOf用于判断 一个对象是否是另一个对象的原型
class Person{
name = "henry";
}
let p = new Person();
console.log(Person.prototype.isPrototypeOf(p)); // true
class Cat{
name = "mm";
}
console.log(Cat.prototype.isPrototypeOf(p)); // false
isPrototypeOf 的注意点
function Person(myName) {
this.name = myName;
}
function Student(myName,myScore) {
Person.call(this,myName);
this.score = myScore;
}
Student.prototype = new Person();
Student.prototype.constructor = Student;
let stu = new Student();
console.log(Person.prototype.isPrototypeOf(stu)); // true
判断属性
- 判断某一个对象是否拥有某一个属性
- in的特点: 只要类中或者原型对象中有, 就会返回true
class Font{
length = 45;
}
Font.prototype.height = 60;
let f = new Font();
console.log("length" in f); // true
console.log("width" in f); // false
console.log("height" in f); // true
- 需求: 判断某一个对象自身是否拥有某一个属性
- 特点: 只会去类中查找有没有, 不会去原型对象中查找
class Font{
length = 45;
}
Font.prototype.height = 60;
let f2 = new Font();
// 特点: 只会去类中查找有没有, 不会去原型对象中查找
console.log(f2.hasOwnProperty("length")); // true
console.log(f2.hasOwnProperty("height")); // false
