What is Object-Oriented Anyway?

Class paradigm:

1. Polymorphism

   • subtyping — instances are substitutable by common super-classes or interfaces/protocols
   • generics — code is written without types (weak) or utilizes subtypes as interfaces/protocols (strong)
   • function overloading — implementations are chosen based on parameter types

2. Encapsulation - a mechanism for restricting or controlling access to an object's components (public / private / privileged)

3. Inheritance - a mechanism of implementation reuse that typical establishes an is-a relationship.

Is JavaScript Object-Oriented?

Three perspectives:

1. Interesting StackOverflow Q&A
2. JavaScript: The World's Most Misunderstood Programming Language — Douglas Crockford
3. Introduction to Object-Oriented JavaScript — MDN

What about CSS or HTML?

For CSS:

• CSS is a declarative language for style.
• It's use can be encapsulated by classes
• whose proper use applies rendering without knowledge of the mechanism (i.e. encapsulation)

For HTML:

• Markup is explicit,
• it is the glue,
• but less markup is better.

Use a combination of scripts and CSS to enable encapsulation and clean content.

TODO List Homework

      ⇓ the class ⇓ and id provide differently scoped access
<div class="todo" id="todo-list">
   <div class="controls"> ⇐ a class can be scoped by a parent class
      <input size="30" class="text"/><button class="add">Add</button><button class="clear">Clear</button>
   </div>   ⇓⇑ class and markup allows navigation of contained markup
   <ol class="list"/>
</div>
         

Markup provides functional overloading:

• its presence
• invokes different implementations
• which results in different behaviors.

Example: Delete the <button class="clear">...</button> and what happens?

TODO List Solution Walk-through

(exercise in class)