Objects in JS

object

One Concrete thing , A group of A disorderly relevant attribute and Method Set , All things are objects

Object by attribute and Method form

• attribute ： Things features , Use in objects attribute Express （ Common nouns ）
• Method ： Things Behavior , Use in objects Method Express （ Common verbs ）

Three ways to create objects

• utilize Literal Create objects
• utilize new object Create objects
• utilize Constructors Create objects

Create an object using literals

Object literal ： Curly braces {} It contains the expression of this specific thing （ object ） Properties and methods of

1. The attributes or methods inside take Key value pair In the form of   key Property name ： value     Property value
2. Multiple attributes or methods are separated by commas
3. The method colon is followed by an anonymous function

utilize new Object Create objects

var obj = new Object();

• Use the equal sign = The method of assignment Add the properties and methods of the object
• Each property and method ends with a semicolon

obj.uname = ' Zhang Sanfeng ';
obj.sex = ' male ';
obj.sayHi = function () {
    console.log('Hi');
}

Using constructors to create objects

reason ： The first two methods of creating objects can only Create a object , Many properties and methods are the same , So using the constructor method , Repeat the same code , Let's put this function It's called a constructor

Because this function is not encapsulated in ordinary code , But the object , Constructor is to abstract the same attributes and methods and encapsulate them into functions

The syntax format of the constructor

function  Constructor name  () {
    this. attribute  =  value ;
    this. Method  = function () {
    
    }
}
// Using functions 
new  Constructor name ();

1、 The constructor name should be capitalized

2、 Constructors don't need return You can return the result

3、 Calling the constructor must use new

4、 as long as new Star（） Calling the function creates an object

5、 Properties and methods must be preceded by this

Use object

（1） Properties of the calling object , take Object name . Property name In the form of   . Understood as

（2） Call the second property Object name [' Property name ']

（3） Method of calling object , Object name . Method name （）     Don't forget the parentheses

Variable 、 attribute 、 function 、 Differences in methods

The same thing ：

The similarities between variables and attributes are used to Store the data Of

Functions and methods are To achieve a function

Difference ：

Variable Make a separate statement And the assignment , When using direct Write variable name （ Exist alone ）

The attribute is Inside the object , yes No declaration required Of , When using, it must be object . attribute Can be used

The function is Make a separate statement , And call the function name （） Exist alone Of

Method , stay Inside the object , Call time object . Method （）

The difference between constructors and objects

An object refers specifically to a Concrete things

Constructor refers to a large class of

The process of creating objects using constructors is also called Object instantiation

new keyword

1. new Constructors can be in memory Create an empty object
2. this will Point to The object just created
3. Execute the code in the constructor , Give constructors add to Properties and methods
4. return This object （ So constructors don't need return）

Traversing objects

for...in You can modify the attributes of arrays or objects loop operation

for （ Variable  in  object ） {
    console.log(k) // The property name of the object 
    console.log( object [k]) // Property value of object     
}

Use for in The variables inside Like to use k perhaps key

Object summary

• Objects can make the structure clearer
• Objects are complex data types object
• The essence ： An object is an unordered collection of related properties and methods
• Constructors generally refer to a large class
• An object instance refers specifically to a thing