constructor call a member function that return a value in javascript

Question

class Car {
  constructor(name, year) {
    this.name = name;
    this.year = year;
    this.age();

  }
  age() {
   return 99;
  }
}

myCar = new Car("Ford", 2014);
document.getElementById("demo").innerHTML =
"My car is " + myCar + " years old.";

//result

My car is [object Object] years old.

why variable myCar did not have value 99 ? instead it contains [object,object]

Answer 1

Taking into account your current code:

class Car {
  constructor(name, year) {
    this.name = name;
    this.year = year;
    this.age();

  }
  age() {
   // date = new Date();  // This will not work
   let date = new Date(); // This will work
   return 99;
  }
}

myCar = new Car("Ford", 2014);
document.getElementById("demo").innerHTML =
"My car is " + myCar + " years old.";

1. myCar is the object. If you want to return 99 you need to call myCar.age()
2. mind that the "age" of a car depends on the current date. My today's 13 year old car can be 14 tomorrow. And with year alone you cannot be fully exact on this.