Mastering TypeScript/

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The super Function and Function Overriding

The super Function and Function Overriding

Learn how to use the super keyword to call base class constructors and method overrides.

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The super function

When using inheritance, it is quite common for a base class and a derived class to implement the same method. This is seen most often with class constructors. If a derived class has a constructor, then this constructor must call the base class constructor using the super keyword, or TypeScript will generate an error as follows:

// Class definition for BaseClassWithCtor
class BaseClassWithCtor {
  // private property to store the id
  private id: number;
  // constructor to initialize the id
  constructor(id: number) {
    this.id = id;
  }
}
// Class definition for DerivedClassWithCtor that extends BaseClassWithCtor
class DerivedClassWithCtor
  extends BaseClassWithCtor {
  // private property to store the name
  private name: string;
  // constructor to initialize the id and name
  constructor(id: number, name: string) {
    // calling the super constructor to initialize the id
    super(id);
    this.name = name;
  }
}
Using the super keyword

  • We define a class named BaseClassWithCtor from lines 2–10 that has a single property named id of type number and also defines a constructor function that initializes this id property.

  • We then define a class named DerivedClassWithCtor from ...

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