Is it legal to assign an instance to a class property?

Question

JavaScript

If I need only one instance for the entire program, it is convenient to write this instance to a class property and then use its methods in the future. Is there any reason why you can't do that? Or is it better to create a new instance each time? For example, my class creates an element during initialization and inserts it into the markup, I only need to create this element once.

class A {
  constructor() {}

  methodA() {
    this.b.methodB();
  }

  init() {
    this.b = new B();
    this.methodA();
  }

}

class B {
  constructor() {}

  methodB() {
           console.log('methodB');
  }
}

Answer 1

Yes, it's allowed.
Only this property of object instead of a class. When you did
foo = new A() // a new object was created, an instance of class A.
bar = new A() // another new object was created, an instance of class A.
// When you do
foo.init() // was created B, registered in the property of the foo object, but at the same time bar has nothing in this property, because it has not yet been init