JavaScript

TS2515: Abstract Member Not Implemented: What It Means and How to Fix It

Error reference

TS2515: Abstract Member Not Implemented

Language

JavaScript

Severity

Medium

When it happens

TypeScript error TS2515 is reported when a concrete (non-abstract) class extends an abstract class but does not implement all of its abstract members.

Potential fixes

Implement all abstract methods in your concrete class. Your IDE will usually show which methods are missing. When adding a new abstract method to a base class, TypeScript will immediately flag all subclasses that need updating.

Deep dive

TypeScript error TS2515 is reported when a concrete (non-abstract) class extends an abstract class but does not implement all of its abstract members. Abstract members define the interface that subclasses must fulfill.

Why it happens

•A subclass is missing an implementation of one or more abstract methods.
•A method was added to the abstract class but not yet added to all subclasses.
•Copy-pasting a class definition without updating the abstract implementations.
•Renaming an abstract method without updating the subclass override.

Potential fixes

Implement all abstract methods in your concrete class. Your IDE will usually show which methods are missing. When adding a new abstract method to a base class, TypeScript will immediately flag all subclasses that need updating.

Examples

JavaScript

Code that triggers the error

abstract class Shape {
  abstract area(): number;
}

class Circle extends Shape {
  // forgot to implement area()
}

Error output

error TS2515: Non-abstract class 'Circle' does not implement inherited abstract member 'area' from class 'Shape'.

Fixed code

abstract class Shape {
  abstract area(): number;
}

class Circle extends Shape {
  constructor(private radius: number) {
    super();
  }
  area(): number {
    return Math.PI * this.radius ** 2;
  }
}

Practice in English

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