Classes are a template for creating objects. They encapsulate data with code to work on that data. Classes in JS are built on prototypes but also have some syntax and semantics that are not shared with ES5 class-like semantics. Classes are in fact "special functions", and just as you can define function expressions and
function declarations, the class syntax has two components: class expressions and class declarations. One way to define a class is using a class declaration. To declare a class, you use the Hoisting An important
difference between function declarations and class declarations is that while functions can be called in code that appears before they are defined, classes must be defined before they can be constructed. Code like the following will throw a
This occurs because while the class is hoisted its values are not initialized. Class expressions A class expression is another way to define a class. Class expressions
can be named or unnamed. The name given to a named class expression is local to the class's body. However, it can be accessed via the
Note: Class expressions must be declared before they can be used (they are subject to the same hoisting restrictions as described in the class declarations section). Class body and method definitions The body of a class is the part that is in curly brackets Strict modeThe body of a class is executed in strict mode, i.e., code written here is subject to stricter syntax for increased performance, some otherwise silent errors will be thrown, and certain keywords are reserved for future versions of ECMAScript. Constructor The constructor method is a special method for creating and initializing an object created with a A constructor can use the Static initialization blocksClass Multiple static blocks can be declared, and these can be interleaved with the declaration of static properties and methods (all static items are evaluated in declaration order). Prototype methodsSee also method definitions.
Generator methodsSee also Iterators and generators.
Static methods and propertiesThe static keyword defines a static method or property for a class. Static members (properties and methods) are called without instantiating their class and cannot be called through a class instance. Static methods are often used to create utility functions for an application, whereas static properties are useful for caches, fixed-configuration, or any other data you don't need to be replicated across instances.
Binding this with prototype and static methods When a static or prototype method is called without a value for
If we rewrite the above using traditional function-based syntax in non–strict mode, then
Instance propertiesInstance properties must be defined inside of class methods:
Field declarationsPublic field declarationsWith the JavaScript field declaration syntax, the above example can be written as:
We don't need keywords like By declaring fields up-front, class definitions become more self-documenting, and the fields are always present. As seen above, the fields can be declared with or without a default value. See public class fields for more information. Private field declarationsUsing private fields, the definition can be refined as below.
It's an error to reference private fields from outside of the class; they can only be read or written within the class body. By defining things that are not visible outside of the class, you ensure that your classes' users can't depend on internals, which may change from version to version. Note: Private fields can only be declared up-front in a field declaration. Private fields cannot be created later through assigning to them, the way that normal properties can. For more information, see private class features. Sub classing with extendsThe
If there is a constructor present in the subclass, it needs to first call super() before using "this". One may also extend traditional function-based "classes":
Note that classes cannot extend regular
(non-constructible) objects. If you want to inherit from a regular object, you can instead use
Species You might
want to return For example, when using methods such as
Super class calls with super The
Mix-insAbstract subclasses or mix-ins are templates for classes. An ECMAScript class can only have a single superclass, so multiple inheritance from tooling classes, for example, is not possible. The functionality must be provided by the superclass. A function with a superclass as input and a subclass extending that superclass as output can be used to implement mix-ins in ECMAScript:
A class that uses these mix-ins can then be written like this:
Re-running a class definition A class can't be redefined. Attempting to do so produces a If you're experimenting with code in a web browser, such as the Firefox Web Console (Tools > Web Developer > Web Console) and you 'Run' a definition of a class with the same name twice, you'll get a Specifications
Browser compatibilityBCD tables only load in the browser See alsoWhich of the following is accessed by member function of class?Explanation: A member function can access it's class member variables, irrespective of the access specifier in which the member variable is declared.So, a member function can always access the data in the class of which it is a member. So, option (A) is correct.
Which of the following is accessed by a member function of a class the object of that class all members of a class?A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. It operates on any object of the class of which it is a member, and has access to all the members of a class for that object.
Which of the following is accessed by a member function of a class Mcq?Explanation: The public member functions of a class can easily access the private data members of the same class. This is achieved by the "friend", which is a non-member function to the class. Its private data can be accessed.
Which of the following can access private data members or member functions of a class?Private: The class members declared as private can be accessed only by the member functions inside the class. They are not allowed to be accessed directly by any object or function outside the class. Only the member functions or the friend functions are allowed to access the private data members of the class.
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