Using TypeScript for abstract methods and polymorphism

What do I need to fix in order for this code to function properly?

abstract class Animal {
    // No constructor
    ...    
    public abstract me():Animal;
}

class Cat extends Animal {
    constructor() {
        super();
    }

    // Why does this not work as expected? Shouldn't every cat be considered an Animal?
    me():Cat {
        return this;
    }
}

An error is encountered:

Type 'this' is not assignable to type 'Animal'.

Answer №1

After some trial and error, I was able to successfully resolve the issue. It appears that failure to properly implement all methods in an abstract class can confuse typescript when determining if a child class is extending the parent.

Another issue I encountered was realizing that 'this' inside a promise callback does not refer to the object instance as expected.

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