JavaScript has drastically improved as a language over the past few years. TypeScript provides some nice features on top of the JavaScript such as static typing. In this post, we are going to cover one of these TypeScript features, the
private
keyword.ES2015 Classes
Abstract Classes. Abstract classes round out TypeScript’s support for hierarchies of this nature. An abstract class looks and feels like a standard class with a key exception: abstract classes may never be instantiated. If JavaScript is your first and primary programming language, this may seem strange. This example introduces the abstract keyword. We now have an abstract class, Base.This abstract class implements the Activatable interface. In doing so, you can see another characteristic of TypeScript's abstract functionality: you may mark classes and class members as abstract. (In fact, you must mark the class abstract if it contains any abstract members). A property should never have a side effect, methods might. Mixing Java style getters with good getters makes the code more confusing.Or is there a pattern in TypeScript that you just can't achieve without abstract properties?We could probably think of some strange edge case where some library expect a good getter but I would say no. TypeScript makes inheritance easy by letting us define abstract classes — where some implementation is done by the abstract and others are done in the subclass that extends the abstract class.
Before we dive into TypeScript’s
private
feature let’s do a quick recap of JavaScript classes. Cod4 mod menu pc. In the new ES2015 standard of JavaScript we get a Object Oriented Class style syntax that looks like the following,Typescript Optional Abstract Property
In this example we are using pure JavaScript no TypeScript syntax or features are being used. JavaScript classes can be exported and used in other JavaScript modules. JavaScript classes also have constructors, properties, and methods similar to most Class-based languages we see today. Unfortunately, in the current version of JavaScript, there is no support for private properties or private methods yet. In JavaScript all class instance properties and methods are public.
TypeScript Private Properties
![Typescript abstract getter Typescript abstract getter](https://resources.jetbrains.com/help/img/dotnet/2020.1/generate_properties_typescript.png)
Using TypeScript, we can add
private
functionality into our classes. What are private properties or methods? A private property of method can only be accessed or called from the class instance itself. Let’s take a look at an example private property.In this example, we are using a typical pattern of a private property to control how a property is updated. In our use case, it is valid to increase the age of a person, but you cannot set it to a random value or a younger age. To enforce this, we create a
private
property _age
. The _age
property is a property that will be only available internally to the class. For example, if I try to set _age
I get an error because it is private to the class. If I try to read _age
I also get the same errorWe can see the
private
hides the property from the user/consumer of the class. If I try to set cory.age
we also get an error because I defined only a get
for the age
property with no set
so this property can only be read-only. We can go one step further and refactor our constructor a little bit more.TypeScript Constructor Assignment
In this example, we can simplify our constructor parameters by combining the declaration and assignment into a single statement.
We can prefix the constructor parameters with the
public
or private
keyword to automatically have TypeScript assign the parameter as a property of the class. In this example, this removes the unnecessary declaration and assignment of both firstName
and lastName
. Makemusic finale 2014 torrent download.TypeScript Private Methods
Methods can also be private which is useful for hiding implementation detail of how a Class works to the user of the Class. Let’s take a look at a minimal example.
Typescript Abstract Static
In this example, we created a private method
log()
. Log can only be called by other methods in our class. You can see above if I try to call log directly, we get a TypeScript error. Private properties and methods can help enforce logic for when data is updated and also enforce encapsulation of our classes. Check out the full working demo in the link below!