Javascript scope usage instructions_javascript tips

Public, protected and private scopes

In traditional object-oriented programming, the main focus is on public and private scopes. Object properties in the public scope can be accessed from outside the object, that is, after developers create an instance of the object, they can use its public properties. The properties in the private scope can only be accessed within the object, that is, they do not exist to the outside world. This also means that if a class defines private properties and methods, those properties and methods cannot be accessed by its subclasses.

Recently, another type of scope has become popular, the protected scope. Although the rules for applying protected scope vary in different languages, generally speaking, it is used to define private properties and methods, but these properties and methods can also be accessed by their subclasses.

It is almost meaningless to discuss these scopes in ECMAScript, because there is only one kind of scope in ECMAScript - public scope. All properties and methods of all objects in ECMAScript are public. Therefore, you must be careful when defining your own classes and objects. Remember, all properties and methods are public by default.

Many developers have proposed effective attribute scope patterns on the Internet to solve this problem of ECMAScript. Due to the lack of private scope, developers developed a convention stating which properties and methods should be considered private. This convention requires that attribute names be preceded and followed by underscores. For example:

In this code, the attribute color is private. Remember, these underscores don't change the fact that these properties are public; they just tell other developers that the property should be treated as private.

Some developers also like to use a single underscore to describe private members, such as obj._color.

Static scope is not static

Properties and methods defined in static scope can be accessed from the same location at any time. In Java, a class can have static properties and methods, which can be accessed without instantiating an object of the class. For example, in the java.net.URLEncoder class, its function encode() is a static method.

Strictly speaking, ECMAScript does not have static scope. However, it can provide properties and methods to the constructor. Remember, constructors are just functions. Functions are objects, and objects can have properties and methods. For example:

Here, the method alternate() is actually the method of function sayHi. You can call sayHi() to output "hi" like a regular function, or you can call sayHi.alternate() to output "hola". Even so, alternate() is a method in the public scope of sayHi(), not a static method.