Is it feasible to incorporate a method into a prototype and ensure that 'this' is associated with the appropriate type in TypeScript?

I have a scenario where I need to add a new method to a prototype, specifically to a class created using TypeScript. Here is an example:

declare module "./MyClass" {
    interface MyClass {
        myNewMethod();
    }
}

MyClass.prototype.myNewMethod = function() {

    let foo = this; // TypeScript doesn't recognize 'foo' as being of type MyClass :-(

}

Unfortunately, TypeScript fails to identify the type of this. Although I could manually declare foo, I prefer not to introduce an extra variable just to work around this TypeScript limitation.

Is there a way to achieve this without creating additional variables?

Answer №1

It's a bit unclear where the class declaration is happening. Nonetheless, this block of code seems to be functioning properly:

class MyClass {
  myNewMethod() {}
}

MyClass.prototype.myNewMethod = function f() {
  const foo = this // foo is correctly typed to MyClass
}

Check out the typescript playground (using typescript 4.7.4)

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