Typescript将泛型传递给Map

Question

I want to pass a generic type from the child class to a property.

interface MyInterface { 
    method(): void;
}

class B<P> {

    entities = new Map<number, P>();
}

class C<P = MyInterface> extends B<P> {

    click() {
      this.entities.get(1).method();
    }
}

I'm expecting each entity to be of type MyInterface , but I'm getting a type error:

Property method() doesn't exist on type P

What is the issue?

Answer 1

Just because P = MyInterface does not mean any passed in P must extend MyInterface . For example with no other constraints, this would also be valid:

new C<{ noMethod() : void }>();

You need to add a constraint to P to say that any passed in P must extend MyInterface , and you can keep MyInterface as a default as well.

interface MyInterface {
  method(): void;
}

class B<P> {

  entities = new Map<number, P>();
}

class C<P extends MyInterface = MyInterface> extends B<P> {

  click() {
    this.entities.get(1).method();
  }
}