Can you use array in javascript without initializing it? [closed]

Ok so I have a code like this, you can skip most of it, I will mark the important part.

const Author = require('./../models/author.model');
const Book = require('./../models/book.model');
class BookRepository {
  constructor() {
    this.seedRepo();
  }
  addBook(title, author, language, publisher, ISBN) {
    this.books.push(
      new Book(title, author, language, publisher, ISBN)
    );
  }
  addAuthor(firstName, lastName, DOB, gender) {
    let newId = this.authors[this.authors.length - 1].id + 1;
    let newAuthor = new Author(newId, firstName, lastName, DOB, gender);
    this.authors.push(newAuthor);
    return newAuthor;
  }
  getLanguage(lang) {
    let language = this.languages.find(l => l.abbrev === lang);
    return language && language.langName || 'unknown?';
  }
  getAuthor(id) {
    for (let a of this.authors) {
      if (a.id === id) return a;
    }
    return null;
  }
  /************ Seeding repo below: ****************/
  seedRepo() {
    this.seedAuthors();
    this.seedBooks();
    this.seedLanguages();
  }
  seedAuthors() {
    this.authors = [];
    this.authors.push(new Author(100, 'Steve', 'McConnel', new Date('1965-07-10'), 'm'));
    this.authors.push(new Author(101, 'Douglas', 'Crockford', new Date('1955-01-01'), 'm'));
    this.authors.push(new Author(201, 'Douglas', 'Adams', new Date('1952-03-11'), 'm'));
    this.authors.push(new Author(202, 'Sylvia', 'Plath', new Date('1932-10-27'), 'f'));
  }
  seedBooks() {
    this.books = [];
    this.addBook('Code Complete', this.getAuthor(100), 'en',
      'Microsoft Press; 2nd edition',
      '0735619670'
    );
    this.addBook('JavaScript: The Good Parts', this.getAuthor(101), 'en',
      `O'Reilly Media`,
      '9780596517748'
    );
    this.addBook(`The Hitchhiker's Guide to the Galaxy`, this.getAuthor(201), 'en',
      'Del Rey; Reissue edition',
      '1535185554'
    );
    this.addBook(`The Bell Jar`, this.getAuthor(202), 'en',
      'Harper Perennial Modern Classics;',
      '0060837020'
    );
  }
  seedLanguages() {
    this.languages = [{
      abbrev: "en",
      langName: "English"
    }, {
      abbrev: "hr",
      langName: "Croatian"
    }];
  }

}



const repoInstance = new BookRepository();

module.exports = repoInstance;

https://www.codepile.net/pile/k8RkQvWN

how can we use array authors and books without initializing it?

Thank you!