简单的 TypeScript 类给出了 TypeError

Question

I want to use class Literal from file Classes.tsx in file App.tsx but TypeScript returns a TypeError even if they're in the same file. Works fine on typescriptlang.org/play .

// Classes.tsx
abstract class Expression {
  abstract val: boolean;
  abstract str: string;
}

class Literal extends Expression {
  val: boolean;
  constructor(value: boolean) {
    super();
    this.val = value;
  }
  get str(): string {
    return this.val ? "W" : "F";
  }
}

// App.tsx
import { Expression, Literal } from "./Classes";

let F: Literal = new Literal(false);

Error: TypeError: Cannot set property str of #<Literal> which has only a getter

Why?

Answer 1

There is two solutions:

1. adding setter
2. change declaration to getter (from abstract str: string; to abstract get str(): string;