javascript基础知识

var person = {
  name : ['Bob', 'Smith'],
  age : 32,
  gender : 'male',
  interests : ['music', 'skiing'],
  bio : function() {
    alert(this.name[0] + ' ' + this.name[1] + ' is ' + this.age + ' years old. He likes ' + this.interests[0] + ' and ' + this.interests[1] + '.');
  },
  greeting: function() {
    alert('Hi! I\'m ' + this.name[0] + '.');
  }
};

person.age // 点号访问法
person["age"] //括号表示法

name : {
  first : 'Bob',
  last : 'Smith'
},

person.name.first
person["name"]["first"]

person.age = 45
person.greeting = function() {
    alert('Hi! I\'m ' + this.name.first + '.');
  }

function Person(name) {
  this.name = name;
  this.greeting = function() {
    alert('Hi! I\'m ' + this.name + '.');
  };
}

var person1 = new Person('Bob'); //
var person2 = new Person('Sarah');

{
  name : 'Bob',
  greeting : function() {
    alert('Hi! I\'m ' + this.name + '.');
  }
}

{
  name : 'Sarah',
  greeting : function() {
    alert('Hi! I\'m ' + this.name + '.');
  }
}

var person1 = new Object(); //首先, 您能使用Object()构造函数来创建一个新对象。 是的， 一般对象都有构造函数，它创建了一个空的对象。

//这样就在person1变量中存储了一个空对象。然后, 可以根据需要, 使用点或括号表示法向此对象添加属性和方法
person1.name = 'Chris';
person1['age'] = 38;
person1.greeting = function() {
  alert('Hi! I\'m ' + this.name + '.');
}

var person1 = new Object({
  name : 'Chris',
  age : 38,
  greeting : function() {
    alert('Hi! I\'m ' + this.name + '.');
  }
});

var person2 = Object.create(person1);

person2.name
person2.greeting()

function doSomething(){}
doSomething.prototype
/*
doSomething 函数有一个默认的原型属性如下：
{
    constructor: ƒ doSomething(),
    __proto__: {
        constructor: ƒ Object(),
        hasOwnProperty: ƒ hasOwnProperty(),
        isPrototypeOf: ƒ isPrototypeOf(),
        propertyIsEnumerable: ƒ propertyIsEnumerable(),
        toLocaleString: ƒ toLocaleString(),
        toString: ƒ toString(),
        valueOf: ƒ valueOf()
    }
}
*/

// 我们可以添加一些属性到 doSomething 的原型上面
doSomething.prototype.foo = "bar"; 

//然后，我们可以使用 new 运算符来在现在的这个原型基础之上，创建一个 doSomething 的实例。
var doSomeInstancing = new doSomething();
doSomeInstancing.prop = "some value"; // add a property onto the object
console.log( doSomeInstancing );
/*
{
    prop: "some value",
    __proto__: {
        foo: "bar",
        constructor: ƒ doSomething(),
        __proto__: {
            constructor: ƒ Object(),
            hasOwnProperty: ƒ hasOwnProperty(),
            isPrototypeOf: ƒ isPrototypeOf(),
            propertyIsEnumerable: ƒ propertyIsEnumerable(),
            toLocaleString: ƒ toLocaleString(),
            toString: ƒ toString(),
            valueOf: ƒ valueOf()
        }
    }
}
*/

doSomeInstancing.__proto__ === doSomething.prototype
//true

person1 ----inherit----> Person.prototype----inherit---->Object.prototype

person1.valueOf === Object.prototype.valueOf 
//true

function Person(name) {
  this.name = name;
  this.greeting = function() {
    alert('Hi! I\'m ' + this.name + '.');
  };
}

> person1 = new Person(); 
< Person {name: undefined, greeting: ƒ}
> person2 = new Person();
< Person {name: undefined, greeting: ƒ}
> person1.greeting == person2.greeting
< false

function Person(name) {
  this.name = name;
}

Person.prototype.greeting = function() {
    alert('Hi! I\'m ' + this.name + '.');
  };

> person1 = new Person(); 
< Person {name: undefined}
> person2 = new Person();
< Person {name: undefined}
> person1.greeting == person2.greeting
< true

> person1.greeting = 'test'
< "test"
> person2.greeting
< ƒ () {
    alert('Hi! I\'m ' + this.name + '.');
  }

> person1.__proto__.greeting = 'test'
< "test"
> person2.greeting
< "test"

var person2 = Object.create(person1);
//create() 实际做的是从指定原型对象创建一个新的对象。这里以 person1 为原型对象创建了 person2 对象。在控制台输入：
person2.__proto__ === person1
// true

person1.constructor === Person
// true

person2 = new person1.constructor("person2");

//给Person动态添加一个方法
Person.prototype.farewell = function() {
  alert(this.name.first + ' has left the building. Bye for now!');
}

person1.farewell();

Person.prototype.fullName = this.name.first + ' ' + this.name.last;

function Person(first, last, age, gender, interests) {
  this.name = {
    first,
    last
  };
  this.age = age;
  this.gender = gender;
  this.interests = interests;
};

//所有的方法都定义在构造器的原型上
Person.prototype.greeting = function() {
  alert('Hi! I\'m ' + this.name.first + '.');
};

function Teacher(first, last, age, gender, interests, subject) {
  Person.call(this, first, last, age, gender, interests);
  this.subject = subject;
}

Teacher.prototype = Object.create(Person.prototype);

Teacher.prototype === Person.prototype
//false
Teacher.prototype.__proto__ === Person.prototype
//true

Teacher.prototype.constructor
// Person
Teacher.prototype.constructor = Teacher;

Teacher.prototype.greeting = function(){
    consol.log('greeting');
}

person.constructor == Person
person.__proto__ == Person.prototype

1. person.__proto__.__proto__ == Object.prototype
2. person.constructor.prototype.__proto__ == Object.prototype

person = {
  "name":'hello'
}

1. person.__proto__ == Object.prototype
2. person.constructor.prototype == Object.prototype

function merge(target, source) {
    for (let key in source) {
        if (key in source && key in target) {
            merge(target[key], source[key])
        } else {
            target[key] = source[key]
        }
    }
}

let o1 = {}
let o2 = {a: 1, "__proto__": {b: 2}}

// let o2 = {a: 1, __proto__: {b: 2}}
merge(o1, o2)
console.log(o1.a, o1.b)

o3 = {}
console.log(o3.b)

let o1 = {}
let o2 = JSON.parse('{"a": 1, "__proto__": {"b": 2}}')
merge(o1, o2)
console.log(o1.a, o1.b)

o3 = {}
console.log(o3.b)