JS Object-Oriented 2

1. History

Machine oriented

Process oriented: Break down the execution of a program into several steps

Object-oriented: Decompose the execution of a program into several things

2. Two basic concepts of object-oriented

Class: Representing a certain kind of thing, is abstract

Object: Represents a thing, is a specific

3. Quick Start

To express a person's complete information

1 <script> 2      3     //Process 4     var name = ' Zhangsan '; 5     var age =; 6     var marry = true; 7     alert (n Ame + age + marry); 8      9     //object-oriented ten     function person{11     }12     var p1 = new Person ();     p1.name = ' Lisi ';     P1.age = 20;15     p1.marry = true;16     alert (p1.name + p1.age + p1.marry);     </script>

In the process-oriented example, we used three variables to define a person's complete information, but these three variables are not necessarily related to each other, such as: I now find the variable age, although the data can be taken, but it is not clear that this is "who" ages.

In an object-oriented example, function person{} is a constructor. We can understand that each defined function person{} is a constructor for the person class.

Common system classes in 4.JS

1) String class

Length: Gets the string length

IndexOf (String): Gets the position where the argument appears in the string

SUBSTR (num1,[num2]): Intercept string

toLowerCase (): Convert to lowercase

toUpperCase (): Convert to uppercase

Replace (STR1,STR2): string substitution

2) Date class

GetYear (): Returns the year (sometimes with an error, the second is recommended)

getFullYear (): Return year

GetMonth (): Return month (0---11)

GetDate (): Returns the day ordinal of a month

GetDay (): Return days (0-6)

GetHours (): Returns the number of hours

Getminutes (): Returns the number of minutes

Getseconds (): Returns the number of seconds

Getmilliseconds (): Returns the number of milliseconds

3) Math class

Ceil (value): Returns the smallest integer greater than or equal to the number (for example, paging Math.ceil (4.8) =5)

Floor (value): Returns the largest integer less than or equal to the number

Min (value 1, value 2): Returns the minimum number

Max (numeric 1, value 2): Returns the maximum number

Pow (value 1, value 2): Returns the value of value 1 2 times Square

Random (): returns 0----------1

Round (value): Rounding

sqrt (value): Open square root

The methods under the math class are static methods

5. Custom class--Definition of class

Grammar:

function class name () {

}

In JS, there is no class definition statement, only function, each function, we can think of it as the constructor of the class of the same name

For example:

function person () {

}

It is the constructor of the person class

This function is also called the constructor

6. Custom classes--declaring objects

Syntax: var object =new class name ();

Keyword NEW: Instantiating an object, opening up the appropriate memory space

1 function person () {2     alert (' Hello '), 3}4 var p1 = new Person ();

When we execute the above example, we find that the person constructor is executed directly at the time of instantiation

7. Custom classes--about the use of object properties

Grammar:

Object. Properties;

Object [' attribute '];

1 function person () {2     alert (' Hello '), 3}4 var p1 = new Person (); 5 p1.name= ' Zhangsan '; 6 p1.age=30;7 alert (p1.name+p1.a GE);

In JS, object properties are dynamically added, and object properties can use "." or ['] these two forms of expression

The properties of an object can be any data type, such as: string, Number, object

8. Three keywords

Constructor: The constructor of the object is returned

typeof: Return Data type

Instanceof: Determines whether an object is an instance of a class

1 function person () {2     alert (' Hello '), 3} 4 var p1 = new Person (), 5 p1.name= ' Zhangsan '; 6 p1.age=30; 7 Alert (P1.name +p1.age); 8  9//Returns the constructor of the P1 object (p1.constructor), 11//Gets the data type of the P1 variable (typeof p1), 13//Determines if P1 is an instance of the person class, alert (P1 instanceof person);

9. The object's representation in memory

1//Example of function person () {3}4 var p1 = new Person (), 5 p1.name= ' Zhangsan '; 6 p1.age=30;7 8 var p2 = new Person (); 9 Alert (P2 . name);

In Example 1, when a P1 object is created, the corresponding heap space is opened for P1, and the name and age properties and values are added to the heap space pointed to by P1, and when the P2 object is created, the corresponding space is also opened for the P2 object, but the heap space pointed to by P2 is empty. So the P2 object does not have the name and age properties.

1//Example 2 2 function person () {3} 4 var p1 = new Person (); 5 P1.name = ' Zhangsan '; 6 p1.age = 30; 7  8 var p2 = p1; 9 alert (p2.name); p2.name = ' Lisi '; alert (p2.name); alert (p1.name);

In Example 2, the address of the heap saved in the P1 stack is assigned to P2, so that P2 also points to the address of the heap memory that P1 points to. Two objects point to the same heap of memory, so changing the properties of an object affects another object.

1//Example 3 2 function person () {3} 4 var p1 = new Person (); 5 P1.name = ' Zhangsan '; 6 p1.age = 30; 7  8 var p2 = p1; 9 alert (p2.name), p2 = null;11 alert (p1.name), alert (p2.name);

In Example 3, p2=null; Represents freeing the stack space occupied by P2, but the P1 space remains, P1 still points to the appropriate heap space, so deleting P2 does not affect P1 objects.

JS Object-Oriented 2