null-confusion.js

// example 1

let libraryInstance = null;

const initLibrary = () => {
  libraryInstance = {
    scrollTo() {
    console.log('scrolling');
  }

};

class Menu {
    constructor(libInstance) {
		this.libInstance = libInstance;
	}

	scrollToElement(element) {
      this.libInstance.scrollTo(element);
  }

}

const menu = new Menu(libraryInstance);
initLibrary();

// example 2

let libraryInstance = {};

const initLibrary = () => {

  libraryInstance.scrollTo = () => {
    console.log('scrolling');
  }

};

class Menu {
    constructor(libInstance) {
		this.libInstance = libInstance;
	}

	scrollToElement(element) {
      this.libInstance.scrollTo(element);
  }

}

const menu = new Menu(libraryInstance);
initLibrary();