Private fields are not inherited by subclasses. The #name field is not accessible in the Student class, so the introduce method will throw an error. To fix this, you can add a getter method to the Person class that returns the value of the #name field.

class Person {
  #name;

  constructor(name) {
    this.#name = name;
  }

  introduce() {
    console.log(`Hello, my name is ${this.#name}.`);
  }

  _getName() {
    return this.#name;
  }
}

class Student extends Person {
  #grade;

  constructor(name, grade) {
    super(name);
    this.#grade = grade;
  }

  introduce() {
    console.log(
      `Hello, my name is ${this._getName()} and I am in grade ${this.#grade}.`
    );
  }
}

const student = new Student("John", 5);
student.introduce();