You Don't Know JS: this & Object Prototypes

Chapter 4. Mixing (Up) “Class” Objects

Following our exploration of objects from the previous chapter, it’s natural that we now turn our attention to object-oriented (OO) programming, with classes. We’ll first look at class orientation as a design pattern, before examining the mechanics of classes: instantiation, inheritance, and (relative) polymorphism.

We’ll see that these concepts don’t really map very naturally to the object mechanism in JS, and the efforts (mixins, etc.) many JavaScript developers expend to overcome such challenges.

Note

This chapter spends quite a bit of time (the first half!) on heavy object-oriented programming theory. We eventually relate these ideas to real concrete JavaScript code in the second half, when we talk about mixins. But there’s a lot of concept and pseudocode to wade through first, so don’t get lost—just stick with it!

Class Theory

Class/inheritance describes a certain form of code organization and architecture—a way of modeling real world problem domains in our software.

OO or class-oriented programming stresses that data intrinsically has associated behavior (of course, different depending on the type and nature of the data!) that operates on it, so proper design is to package up (aka encapsulate) the data and the behavior together. This is sometimes called data structures in formal computer science.

For example, a series of characters that represents a word or phrase is usually called a string. The characters are the data. But you almost never ...