JavaScript Tutorial: Getting to Know Objects for the First Time

The JavaScript language is Object-Based, not object-oriented. The reason why it is said to be an object-based language is mainly because it does not provide many functions related to object-oriented languages ​​such as abstraction, inheritance, and overloading. Instead, it unifies complex objects created in other languages ​​to form a very powerful object system.

Although the JavaScript language is object-based, it still has some basic object-oriented characteristics. It can create its own objects as needed, further expanding the scope of JavaScript and enhancing the writing of powerful Web documents.

Basic knowledge of objects

1. Basic structure of objects

Objects in JavaScript are composed of two basic elements: properties and methods. The former means that the object realizes the loading unit of information in the process of implementing its required behavior and is thus associated with variables; the latter means that the object can be executed according to the designer's intention and is thus associated with a specific function.

2. Ways of referencing objects

To actually use an object, it can be obtained in the following ways: referencing JavaScript internal objects, providing them in the browser environment, and creating new objects. This means that before an object is referenced, the object must exist, otherwise the reference will be meaningless and an error message will appear. From the above we can see that JavaScript reference objects can be obtained in three ways. Either create new objects or use existing ones.

3. Regarding object operation statements

JavaScript is not a purely object-oriented language. It has many functions that provide an object-oriented language. Therefore, JavaScript designers call it "object-based" rather than object-oriented. JavaScript provides several statements, keywords, and operators for manipulating objects.

For...in statement

The format is as follows:

For (object attribute name in known object name)

Explanation: 1. The function of this statement is to control the operation of all attributes of the known object cycle. It is to repeatedly set all the properties of a known object to a variable; rather than using a counter to achieve it. 2. The advantage of this statement is that it can be operated without knowing the number of attributes in the object.

with statement

Using this statement means: Within the body of the statement, any reference to a variable is considered a property of this object to save some code.

The format is as follows:

with object{

...}

All statements in curly braces after the with statement are in the scope of the following object object.

this keyword

this is a reference to the current one. In JavaScript, since object references are multi-level and multi-directional, a reference to one object often requires a reference to another object, and another object may require a reference to another object. Referring to another object may cause confusion. In the end, you no longer know which object you are referring to. For this reason, JavaScript provides a statement this for specifying the object as the current object.

New operator

Although the function of objects in JavaScript is already very powerful. But even more powerful is that designers can create their own objects on demand to meet a specific requirement. Use the New operator to create a new object. The object created uses the following format:

Newobject = new Object(Parameters table);

where Newobject creates a new object: object is an existing object; parameters table parameter table; new is a command statement in JavaScript.

4. Reference to object attributes

References to object attributes can be implemented in one of the following three ways:

1. Use the dot (.) operator

university.Name = "Yunnan Province"

university .city="Kunming City"

university.Date="1999"

where university is an existing object, Name, City, and Date are its three attributes, and they are assigned values ​​through operations.

2. Implement reference through the subscript of the object

university[0]="Yunnan"

university[1]="Kunming City"

university[2]="1999"

Access properties through array form , whose value can be obtained using a loop operation.

3. Realize in the form of string

university["Name"]="Yunnan"

university["City"]="Kunming City"

university["Date"]="1999"

5. References to object methods

References to object methods in JavaScript are very simple.

Format: ObjectName.methods()

In fact, methods()=FunctionName method is essentially a function. If you refer to the showmy() method in the university object, you can use:

document.write (university.showmy()) or document.write(university)

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