Objects are usually created to represent entities of the real world, like users, orders and so on: Show
And, in the real world, a user can act: select something from the shopping cart, login, logout etc. Actions are represented in JavaScript by functions in properties. Method examplesFor a start, let’s teach the
Here we’ve just used a Function Expression to create a function and assign it to the property Then we can call it as A function that is a property of an object is called its method. So, here we’ve got a method
Of course, we could use a pre-declared function as a method, like this:
Object-oriented programming When we write our code using objects to represent entities, that’s called object-oriented programming, in short: “OOP”. OOP is a big thing, an interesting science of its own. How to choose the right entities? How to organize the interaction between them? That’s architecture, and there are great books on that topic, like “Design Patterns: Elements of Reusable Object-Oriented Software” by E. Gamma, R. Helm, R. Johnson, J. Vissides or “Object-Oriented Analysis and Design with Applications” by G. Booch, and more. Method shorthandThere exists a shorter syntax for methods in an object literal:
As demonstrated, we can omit To tell the truth, the notations are not fully identical. There are subtle differences related to object inheritance (to be covered later), but for now they do not matter. In almost all cases, the shorter syntax is preferred. “this” in methodsIt’s common that an object method needs to access the information stored in the object to do its job. For instance, the code inside To access the object, a method can use the
The value of For instance:
Here during the execution of Technically, it’s also possible to access the object without
…But such code is unreliable. If we decide to copy That’s demonstrated below:
If we used
“this” is not boundIn JavaScript, keyword There’s no syntax error in the following example:
The value of For instance, here the same function is assigned to two different objects and has different “this” in the calls:
The rule is simple: if Calling without an object: We can even call the function without an object at all:
In this case In non-strict mode the value of Usually such call is a programming error. If there’s The consequences of unbound If you come from another programming language, then you are probably used to the idea of a "bound
In JavaScript The concept of run-time evaluated Here our position is not to judge whether this language design decision is good or bad. We’ll understand how to work with it, how to get benefits and avoid problems. Arrow functions have no “this”Arrow functions are special: they don’t have their “own” For instance, here
That’s a special feature of arrow functions, it’s useful when we actually do not want to have a separate Summary
The value of
Please note that arrow functions are special: they have no What are the two things that an object has that are being utilized in a program?Rather than structure programs as code and data, an object-oriented system integrates the two using the concept of an "object". An object has state (data) and behavior (code). Objects can correspond to things found in the real world. So for example, a graphics program will have objects such as circle, square, menu.
What are objects used for in programming?An object stores its state in fields (variables in some programming languages) and exposes its behavior through methods (functions in some programming languages). Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication.
What are the two characteristics of an object?Characteristics of Objects. An object has identity (each object is a distinct individual).. An object has state (it has various properties, which might change).. An object has behavior (it can do things and can have things done to it).. What is necessary before an object can be used in a program?In order to work with the object in code, you need some way to refer to the object. That's where the reference variable comes in. The reference variable doesn't hold an actual piece of data that your program will work with. Instead, it holds the object's memory address.
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