Learn TypeScript 3 by Building Web Applications

Implementing the removeBook method

The last remaining method is easier to implement.

First, let's again add some validations:

removeBook(collectionIdentifier: string, bookIdentifier: string): void {    if (!collectionIdentifier) {        throw new Error("The collection identifier is required to         remove a book!");    }    if(!bookIdentifier) {        throw new Error("The book identifier is required to remove a         book");    }    console.log(`Removing book ${bookIdentifier} which should be part     of collection ${collectionIdentifier}`);    const existingCollection =     this._bookCollections.get(collectionIdentifier);    if (!existingCollection) {        throw new Error("The collection couldn't be retrieved or we         could not get the book details from the view!");    } // Add the rest of the ...