Exercises: Objects with Methods

The Cat

Write yourself a virtual cat - animals with a CLI are so much nicer than ones with fur.

• Create an object that represents a cat. It should have properties for tiredness, hunger, lonliness and happiness
• Next, write methods that increase and decrease those properties (there's an example in the slides). Call them something that actually represents what would increase or decrease these things, like "feed", "sleep", or "pet".
• Last, write a method that prints out the cat's status in each area.
• Bonus: Make the functions take arguments that increase or decrease arbitrary amounts
• Bonus: Make the functions as arbitrary as cats are - sometimes make it so the cat doesn't want to be petted.

See Solution

var cat = {
  tiredness: 0,
  hunger: 0,
  lonliness: 0,
  happiness: 0,
  play: function() {
    this.hunger += 5;
    this.hunger += 5;
    this.happiness += 20;
  },
  eat: function() {
    this.hunger -= 5;
    this.happiness += 5;
  },
  pet: function() {
    this.lonliness -= 5;
    this.tiredness += 5
  },
  sleep: function {
    this.tiredness -= 5;
  }
}

The Reading List

An object-oriented book-list!

• Create a class through the constructor invocation pattern. BookList = function() {}
  • BookLists should have the following properties:
  • Number of books marked as read (eg, BookList.booksRead)
  • Number of books marked not read yet
  • Next book to read(book object)(eg, BookList.nextBook() - returns a Book)
  • Current book being read (book object)
  • Last book read(book object)
  • An array of all the Books (eg BookList.bookShelf - is an array.)
• Create another class called Book. Book = function() {}
  • Each book should have several properties:
  • Title, Genre, Author
  • Read (true or false)
  • Read date, can be blank, otherwise needs to be a JS Date() object
• Every Booklist should have a few methods:
  • .add(book) - should add a book to the books list.
  • .finishCurrentBook()
    • Should mark the book that is currently being read as read
    • Give it a read date of new Date(Date.now())
    • Change the .lastBook property to be the book that just got finished
    • Change the .currentBook property to point to what's in the .nextBook property
    • Change the .nextBook property to be the first unread book you find in the list of books
• Booklists and Books might need more methods than that. Try to think of more that might be useful.

See Solution

  // This isn't the whole solution - just a really, really big hint.

    var Book = function(title, genre, author, read, readdate) {
      this.title = title || "No Title";
      this.genre = genre "Fiction";
      this.author = author || "No Author";
      this.read = read || False; //short circuit evaluation makes this work as a default
      this.readDate = new Date(readdate);
    } 

    var BookList = function(books) {
      //books should be an array.
      if (!typeof books == "array") {
        books = false;
      }
      this.bookShelf = books || [];

      //check to see if we have books to process
      if (this.bookShelf.length > 0) {
      //Loop through all of the books in the "books" argument
          //Use the .add function to handle adding books, so we keep counts updated.
        
      } 

      this.add = function(book){
        this.bookShelf.push(book);
        //If a book has been read:
          //See if we have a .lastBook property - set if we don't.
          //Update the count of read books
        //If a book hasn't been read:
          //See if we have a .currentBook property. Set if we don't.
          //See if we have a .nextBook property as well - if we didn't set the .currentBook property, set the .nextBook property.
        //it should also update the number of books marked as read / unread
      }
      this.finishCurrentBook = function(){
        //We're going to have to modify the state of this thing pretty heavily.
        if (this.currentBook) {
          this.currentBook.read = true;
          this.lastBook = this.currentBook
          this.currentBook = this.nextBook
          // Now, we need to loop through and get the next book in the array that has read marked as "false"
          //we also need to go through and update the number of books marked as read, and as not read.
        } else {
          //error handling - put something here that says "you don't have a current book!"
        }
      }
    }