Contents
- TypeScript – Method Overriding
TypeScript has abstract classes, which are classes that have partial implementation of a class and in which other classes can be derived from. They can’t be instantiated directly. TypeScript does not have 'abstract' classes as such. But because of structural typing, interfaces are somewhat weak. One cannot for example assert that x instanceof Y, when Yis an interface.
TypeScript - ReadOnly. TypeScript includes the readonly keyword that makes a property as read-only in the class, type or interface. Prefix readonly is used to make a property as read-only. Read-only members can be accessed outside the class, but their value cannot be changed. TypeDoc runs the TypeScript compiler and extracts type information from the generated compiler symbols. Therefore you don’t have to include additional metadata within your comments, TypeScript specific elements like classes, enumerations or property. Abstract classes are base classes from which other classes may be derived. They may not be instantiated directly. Unlike an interface, an abstract class may contain implementation details for its members. The abstract keyword is used to define abstract classes as well as abstract methods within an abstract class.
TypeScript – Method Overriding
Method Overriding is a process of overthrowing a method of super class by method of same name and parameters in sub class.
Method Overriding is useful when sub class wants to modify the behavior of super class for certain tasks.
Example
Following is a simple example of method overriding where eat() method of Student class overrides the eat() method of Person class.
classPerson{ console.log(this.name+' eats when hungry.') } classStudentextendsPerson{ rollnumber:number; // constructors super(); // calling Parent's constructor this.name=name1 displayInformation():void{ console.log('Name : '+this.name+', Roll Number : '+this.rollnumber) eat():void{ } student1.eat() |
When the above .ts program is compiled to .js file.
var__extends= (this&&this.__extends) || (function () { ({ __proto__: [] } instanceofArray&&function (d, b) { d.__proto__=b; }) || function (d, b) { for (varpinb) if (b.hasOwnProperty(p)) d[p] =b[p]; }; extendStatics(d, b); d.prototype=bnull ? Object.create(b) : (__.prototype=b.prototype, new__()); })(); functionPerson() { Person.prototype.eat=function () { }; }()); __extends(Student, _super); functionStudent(rollnumber, name1) { _this.rollnumber=rollnumber; return_this; // functions Student.prototype.displayInformation=function () { console.log('Name : '+this.name+', Roll Number : '+this.rollnumber); // overriding super class method console.log(this.name+' eats during break.'); returnStudent; varstudent1=newStudent(2, 'Rohit'); student1.eat(); |
You can execute .js file using a try javascript online editor by copying the javascript code to the code editor,
Name:Rohit, Roll Number:2 |
Call Super Class Methods from Sub-Class
Immediate super class methods could be called from sub class using super keyword. Virtual piano for mac free download.
eat():void{ console.log(this.name+' eats during break.') |
Replace this method with that of in Student class and run the program.
The eat() method in Person class is executed for super.eat().
Conclusion
In this TypeScript Tutorial, we have learnt to override the behavior of parent classes using Method Overriding with the help of Example TypeScript program.
ES6 includes static members and so does TypeScript. The static members of a class are accessed using the class name and dot notation, without creating an object e.g. <ClassName>.<StaticMember>.
The static members can be defined by using the keyword static. Consider the following example of a class with static property.
The above
Circle
class includes a static property pi
. This can be accessed using Circle.pi
. TypeScript will generate the following JavaScript code for the above Circle
class. The following example defines a class with static property and method and how to access it.
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The above
Circle
class includes a static property and a static method. Inside the static method calculateArea
, the static property can be accessed using this keyword or using the class name Circle.pi
. Typescript Abstract Classes Constructor
Now, consider the following example with static and non-static members.
As you can see, static and non-static fields with the same name can exists without any error. The static field will be accessed using dot notation and the non-static field can be accessed using an object.
Let's see another example.
Typescript Abstract Property Management
In the above example, the
Circle
class includes static method calculateArea
and non-static method calculateCircumference
. As you can see, the static field pi
can be accessed in the static method using this.pi
and in the non-static (instance) method using Circle.pi
. The class or constructor cannot be static in TypeScript.