The difference in property binding order between TypeScript and Babel

problem.ts

class Foo {
  constructor(public namespaces: string[]) {
    this.namespaces = namespaces;
  }

  options = {
    ns: this.namespaces
  };

  get opts() {
    return ({
      ns: this.namespaces
    })
  }
}

console.log(
  new Foo([]).namespaces, // []

  /**
   * TypeScript: []
   * Babel: undefined
   */
  new Foo([]).options.ns,
  new Foo([]).opts.ns
)

solution.ts

class Foo {
  public namespaces: string[];

  constructor(namespaces: string[]) {
    this.namespaces = namespaces;
  }

  options = {
    // Compile-time error (as it should)
    // Property 'namespaces' is used before its initialization.(2729)
    ns: this.namespaces
  };

  get opts() {
    return ({
      ns: this.namespaces
    })
  }
}

console.log(
  new Foo([]).namespaces, // []
  new Foo([]).options.ns, // undefined
  new Foo([]).opts.ns // []
)