JavaScript高级程序设计(第4版)读书分享笔记记录

适用于刚入门前端的同志

创建Object的实例

let person = new Object(); 
person.name = "Nicholas"; 
person.age = 29; 
person.job = "Software Engineer"; 
person.sayName = function() { 
 console.log(this.name); 
};

对象字面量     

let Person = {
    name:'Tom',
    age:28,
    job:'Teacher',
    sayName(){
        console.log(this.name)
    }
}
Person.sayName() // Tom

    虽然使用 Object 构造函数或对象字面量可以方便地创建对象，但这些方式也有明显不足：创建具有同样接口的多个对象需要重复编写很多代码。

工厂模式

function createPerson(name,age,job){
    let o = new Object();
    o.name = name;
    o.age = age;
    o.job = job;
    o.sayName = function(){
        console.log(this.name)
    }
    return o;
}

let person1 = createPerson('Tom',28,'Teacher')
let person2 = createPerson('Jerry',18,'Student')
console.log(person1 ) // {name:'Tom',age:28,job:'Teacher',sayName: ƒ ()}

function Person(name,age,job){
    this.name = name
    this.age = age
    this.job = job
    this.sayName = function(){
        console.log(this.name)
    }
    
}

let person1 = new Person('Tom',28,'Teacher')
person1.sayName () //Tom

let person2 = new Person('Jerry',18,'Student')
person1.sayName () //Jerry

function Person(name, age, job){ 
 this.name = name; 
 this.age = age; 
 this.job = job; 
 this.sayName = sayName; 
} 
function sayName() { 
 console.log(this.name); 
} 
let person1 = new Person("Nicholas", 29, "Software Engineer"); 
let person2 = new Person("Greg", 27, "Doctor"); 
person1.sayName(); // Nicholas 
person2.sayName(); // Greg

function Person(){}
Person.prototype.name = 'Tom'
Person.prototype.age = 28
Person.prototype.job = 'Teacher'
Person.prototype.sayName = function(){
    console.log(this.name)
}

let person1 = new Person()
person1.sayName() // Tom

let person2 = new Person()
person1.sayName() // Tom

console.log(person1.sayName == person2.sayName); // true

         在自定义构造函数时，原型对象默认只会获得 constructor 属性，其他的所有方法都继承自
 Object。每次调用构造函数创建一个新实例，这个实例的内部[[Prototype]]（__proto__属性）指针就会被赋值为构造函数的原型对象

console.log(Person.prototype.__proto__ === Object.prototype); // true

 原型层级

        当访问某个实例的属性和方法时，会先在实例上搜索个属性。如果这个属性在实例上存在，所以就不会再搜索原型对象了。而并没有在实例上找到这个属性，所以会继续搜索原型对象并使用定义在原型上的属性。

例子：

function Person() {} 
Person.prototype.name = "Nicholas"; 
Person.prototype.age = 29; 
Person.prototype.job = "Software Engineer"; 
Person.prototype.sayName = function() { 
 console.log(this.name); 
}; 
let person1 = new Person(); 
let person2 = new Person(); 
person1.name = "Greg"; 
console.log(person1.name); // "Greg"，来自实例
console.log(person2.name); // "Nicholas"，来自原型

例子：

function Person() {} 
Person.prototype.name = "Nicholas"; 
Person.prototype.age = 29; 
Person.prototype.job = "Software Engineer"; 
Person.prototype.sayName = function() { 
 console.log(this.name); 
}; 
let person1 = new Person(); 
let person2 = new Person(); 
person1.name = "Greg"; 

console.log(person1.name); // "Greg"，来自实例
console.log(person2.name); // "Nicholas"，来自原型

delete person1.name; 
console.log(person1.name); // "Nicholas"，来自原型

function Person() {} 
Person.prototype.name = "Nicholas";
Person.prototype.age = 29; 
Person.prototype.job = "Software Engineer"; 
Person.prototype.sayName = function() { 
 console.log(this.name); 
};

let person1 = new Person(); 
let person2 = new Person(); 

console.log(person1.hasOwnProperty("name")); // false

person1.name = "Greg"; 
console.log(person1.name); // "Greg"，来自实例
console.log(person1.hasOwnProperty("name")); // true

// 原型对象还是接上面的

let person = new Person(); 
console.log(hasPrototypeProperty(person, "name")); // true 

person.name = "Greg"; 
console.log(hasPrototypeProperty(person, "name")); // false

//原型对象接上面的案例

let keys = Object.keys(Person.prototype); 
console.log(keys); // "name,age,job,sayName" 

let p1 = new Person(); 
p1.name = "Rob"; 
p1.age = 31; 
let p1keys = Object.keys(p1); 
console.log(p1keys); // "[name,age]"

let keys = Object.getOwnPropertyNames(Person.prototype); 
console.log(keys); // "[constructor,name,age,job,sayName]"

 const o ={
    foo: 'bar', 
     baz: 1, 
     qux: {} 
}; 

console.log(Object.values(o)); // ["bar", 1, {}]
console.log(Object.entries((o))); // [["foo", "bar"], ["baz", 1], ["qux", {}]]