function Person(name) {
    this.name = name; 
}
Person.prototype.getName = function() {
  return this.name;
}
name = 'global';
let peter = new Person('peter');
let john = new Person('john');
// what are the outputs?
john.getName();
john.getName.call(john);
john.getName.call(peter);
john.getName.call(null);

You should get:

john
john
peter
global