recently read ide" rel=" nofollow noreferrer "> functional programming Guide

I can"t understand the part of the container. There is a code that says Functor as follows:

class Maybe {
  static of(x) {
    console.log(1);
    return new Maybe(x);
  }

  get isNothing() {
    console.log(2);
    return this.$value === null || this.$value === undefined;
  }

  constructor(x) {
    console.log(3);
    this.$value = x;
  }

  map(fn) {
    console.log(4);
    return this.isNothing ? this : Maybe.of(fn(this.$value));
  }

  inspect() {
    console.log(5);
    return this.isNothing ? "Nothing" : `Just(${this.$value})`;
  }
}

var test1 = Maybe.of("Malkovich Malkovich");
console.log(test1);

var test2 = Maybe.of(null).map(_.match(/a/ig));
console.log(test2);

var test3 = Maybe.of({ name: "Boris" })
                  .map(_.prop("age"))
                  .map(_.add(10));
console.log(test3);

var test4 = Maybe.of({ name: "Boris", age: 14 })
                  .map(_.prop("age"))
                  .map(_.add(10));
console.log(test4);

what is strange and incomprehensible is how the inspect function is executed? There seems to be no place to call this function.
I hope there is a great god who can answer and communicate with me.