Losing the value of this keyword when using it with instance level variables in a class in javascript

I have two classes one of them is the parent class and the other one is the child class and what I’m trying to achieve is to access the values of child classe’s instance level variables by using this keyword in a field that is declared in the parent class. But when I try to do so it returns undefined. Can anyone please explain what might be going wrong here. Below I’ve pasted a code snippet for your reference. Thanks!

class Parent {
  someField = {
     someValue: 'Values are ::: '+ this.value1 + ' ' + this.value2,
     childType2: "Some gibberish"
   }

  initialize(childType1) {
     this.someField = this.someField[childType1];
  }
}

class Child extends Parent {
   value1 = "someValue 1"
   value2 = "someValue 2"
} 

const child = new Child();
child.initialize("someValue");
console.log(child.someField);