Code each class of the JS class model as an ES2015 class with implicit getters and setters:

These steps are discussed in more detail in the following sections.

For the multi-valued reference property Book::authors, we need to code the operations addAuthor and removeAuthor. Both operations accept one parameter denoting an author either by ID reference (the author ID as integer or string) or by an object reference. The code of addAuthor is as follows:

addAuthor( a) {
  // a can be an ID reference or an object reference
  const author_id = (typeof a !== "object") ? parseInt( a) : a.authorId;
  const validationResult = Book.checkAuthor( author_id);
  if (author_id && validationResult instanceof NoConstraintViolation) {
    // add the new author reference
    let key = String( author_id);
    this._authors[key] = Author.instances[key];
  } else {
    throw validationResult;
  }
}

In the removeAuthor method, the author reference is first checked and, if no constraint violation is detected, the corresponding entry in the map this._authors is deleted:

removeAuthor( a) {
  // a can be an ID reference or an object reference
  const author_id = (typeof a !== "object") ? 
      parseInt( a) : a.authorId;
  const validationResult = Book.checkAuthor( author_id);
  if (validationResult instanceof NoConstraintViolation) {
    // delete the author reference
    delete this._authors[author_id];
  } else {
    throw validationResult;
  }
}

For assigning an array of ID references, or a map of object references, to the property Book::authors, the method setAuthors adds them one by one with the help of addAuthor:

set authors( a) {
  this._authors = {};
  if (Array.isArray(a)) {  // array of IdRefs
    for (let idRef of a) {
      this.addAuthor( idRef);
    }
  } else {  // map of IdRefs to object references
    for (let idRef of Object.keys( a)) {
      this.addAuthor( a[idRef]);
    }
  }
}

For the reference property Book::authors, we have to choose and implement a deletion policy in the destroy method of the Author class. We have to choose between

For simplicity, we go for the second option. This is shown in the following code of the static Author.destroy method where for all concerned book objects the author reference book.authors[authorKey] is dropped:

Author.destroy = function (authorId) {
  const author = Author.instances[authorId];
  // delete all dependent book records
  for (let isbn of Object.keys( Book.instances)) {
    let book = Book.instances[isbn];
    if (book.authors[authorId]) delete book.authors[authorId];
  }
  // delete the author object
  delete Author.instances[authorId];
  console.log("Author " + author.name + " deleted.");
};

We need a serialization function toString() for converting an object to a human-readable string representation that can be used for showing an object in a user interface, and an object-to-record mapping function toRecord() converting a typed object to a corresponding record that can be saved in a persistent datastore. In both cases, internal object references are converted to ID references.

The Book::toString() function creates a string representation that may only contain the relevant properties. The simplest method for showing a set of associated objects, like the authors of a book, is creating a comma-separated list of IDs:

toString() {
  var bookStr = `Book{ ISBN: ${this.isbn}, title: ${this.title},` +
      `year: ${this.year}`;
  if (this.publisher) bookStr += `, publisher: ${this.publisher.name}`;
  return bookStr +", authors:" + 
      Object.keys( this.authors).join(",") +"}";
}

The Book::toRecord() function needs to serialize all property slots of an object. This includes deleting the underscore prefix for obtaining the corresponding record field name:

toRecord() {
  var rec = {};
  for (let p of Object.keys( this)) {
    // copy only property slots with underscore prefix
    if (p.charAt(0) !== "_") continue;
    switch (p) {
    case "_publisher":
      // convert object reference to ID reference
      if (this._publisher) rec.publisher_id = this._publisher.name;
      break;
    case "_authors":
      // convert map of object references to list of ID references
      rec.authorIdRefs = [];
      Object.keys( this.authors).forEach( authorIdStr => {
        rec.authorIdRefs.push( parseInt( authorIdStr));
      });
      break;
    default:
      // remove underscore prefix
      rec[p.substr(1)] = this[p];
    }
  }
  return rec;
}