JavaScript study notes (7) create objects

• object
• Three ways to create an object: ① object literal ② new Object() ③ constructor, new constructor()
• new keyword
• iterate over object properties

1. Create an object

1. Create objects using object literals

        //1.利用字面量创建对象
        var obj ={
            uname: '小明',
            age:18,
            sex:'男',
            sayHi:function(){
                console.log('hi')
            }
        }
        //调用对象的属性
        console.log(obj.sayHi)
        console.log(obj['age'])
        //调用对象的方法
        obj.sayHi()

①The attribute values ​​inside are in the form of key-value pairs, key attribute name: value attribute value

The method colon is followed by an anonymous function

② Object used: object name. attribute name

                        ObjectName['PropertyName']

                        ObjectName.MethodName()

2. Variables, properties, functions, methods

①Variable: declare and assign value separately, directly write the variable name to exist alone when using it

②Properties: In the object, there is no need to declare, and the object.property must be used when using

③Function: It is declared separately, and calls the function name (), exists alone

④ Method: In the object, when calling object. method ()

⑤Constructor: generally refers to a certain category, which is similar to the class in java

⑥Object: specifically refers to a specific thing Andy Lau=={name:'Andy Lau',age:18………}

3. Use new Object to create objects

        //利用new object创建对象
        var obj = new Object()
        obj.age = 18
        obj.name = '男'
        obj.sayHello = function(){
            console.log('hello');
        }
        console.log(obj.age);
        obj.sayHello()

4. Create objects using constructors

The previous two methods of creating objects can only create one object at a time

The constructor is to abstract the same properties and methods in the object and encapsulate them in the function

Grammar format:

        function star(uname,age,sex){
            this.name = uname
            this.age = age
            this.sex = sex
            this.sing = function(song){
                console.log(song);
            }
        }
        var ldh = new star('刘德华',18,'男')
        console.log(ldh.name)
        console.log(ldh['sex'])
        ldh.sing('冰雨')
        console.log(typeof(ldh))

Notice:

1. The first letter of the constructor name should be capitalized (customary)

2. The constructor can return the result without return

3. Calling the constructor must use new

4. We create an object ldh{} as long as new Star() calls the function

5. Using constructors to create objects is also called object instantiation

2. Keyword new

1. New keyword execution process

①The new constructor creates an empty object in memory

②this will point to the empty object just created

③ Execute the code in the constructor and add properties and methods to this empty object

④Returning this object is also the reason why you don’t need to write return

Third, traverse the object properties

        for(var k in ldh){
            console.log(k);  //k，输出的是属性名
            console.log(ldh[k]);  //k是个变量，不加引号
        }

Output :