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Customers who bought this item also bought. Stock Image. Published by No Starch Press We repeat that for the variable water and take a similar path to create a variable basket. After you have added these products to your basket, you finally print out the total amount you have to pay.
Object-oriented programming — the basics
The code inside the function is the constructor. This code executes each time an object is instantiated. Each new object stores these values inside it. Furthermore, we can define functions that the object will provide. We define these function by prepending the this keyword which makes them accessible from the outside see Encapsulation.http://uinstroi.ru/components/271/1476.php
Notice that the functions have full access to the properties. Instantiating a new Basket object simply generates an empty list of products that the program can fill afterwards.
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Mind the assignment of the properties to the variable this. Unfortunately, you have now given full access to the properties from the outside. So everybody could access and modify it:.
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What would happen if you added validation code to prevent, for example, prices less than zero? Any code that accesses the price property directly would bypass the validation. This could introduce errors that would be difficult to trace. Objects should have exclusive control over their data. The only way to access the data is indirect via the functions written into the objects. Data and processing aka logic belong together.
This is especially true when it comes to larger applications where it is very important that processing data is restricted to specifically-defined places. Done right, OOP produces modularity by design, the holy grail in software development. Looking at the above sample, you can see that it does adhere to the module pattern. TypeScript supports single inheritance.
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There is no formal mechanism for creating an abstract class in TypeScript, although a request to implement abstraction in TypeScript has been issued. Not to worry, for now we can use interfaces as a way to abstract class members. For example, a bank might have an Fee interface their favorite one!
When classes implement these interfaces, they must implement all of the members of the interface, as interfaces serve as digital contracts that classes can adhere to. TypeScript enables polymorphism via method overrides as you can see in the example below. In the child classes, we can override these methods and add our own business logic customizations, such as waving a fee if the balance is more than a specified amount. In this case, we overrided the ChargeFee that was originally part of the Fee interface.
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