how to know in which class instances create of anither class in js code example

Example 1: javascript class

// Improved formatting of Spotted Tailed Quoll's answer
class Person {
	constructor(name, age) {
		this.name = name;
		this.age = age;
	}
	introduction() {
		return `My name is ${name} and I am ${age} years old!`;
	}
}

let john = new Person("John Smith", 18);
console.log(john.introduction());

Example 2: javascript classes

let Person = class {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}