Arrays and Objects

Mithat Konar

Arrays

You can create an array using an array literal: a pair of square brackets with a comma-separated list of values in between.
Arrays can be assigned to variables.
You can also create an array using the array constructor:
Each “thing” in an array is an element.
Elements in an array can be of any type:
The typical way of accessing an element is by using square brackets:
The number by which you refer to an element is the index or subscript.
Index numbering starts from zero, not 1.
An array knows how many elements it has in it:
This makes it easy to move element by element through an array:

You can add elements to an array by assigning something to an element beyond the end of the array:
If you add something far beyond the end, extra elements are undefined:
There are also array methods (a kind of function, see Objects below) that let you add elements:
There are corresponding array methods that let you remove elements:

There are lots of other methods that you can use with arrays that are worth looking over.

You can think of objects as being similar to arrays except that you use identifiers to refer to the different parts of the structure instead of a numeric index.

Object literals are defined using curly brackets and a comma-separated list of key:value pairs.
Each key:value pair in the structure is a member.
You access the value of a member using dot notation: <object-name>.<key>
You can also access members using square-bracket array notation with a string as the index.
Keys can be any string. But if you want to use dot notation, keys must use the same name rules that apply to variables and functions.
Values can be anything: numbers, strings, Booleans, arrays, functions, other objects …
You can also create an object using the generic Object constructor (see below) and then add members manually:
This is the same as using an empty object literal, which is generally thought to be better:
You can add members on the fly no matter how you created the object:

Objects are often used used to create a structure that describes something in terms of properties.
You can attach functions to an object as well. A function attached to an object is a method. The functions are usually defined with function literals.
Within a method, you can use the this keyword to refer to a member in the object.
Being able to define a structures that encapsulate a thing’s state (properties) and behavior (methods) is incredibly useful.

Below is a game built using basic object-oriented principles.
We define the requisiteWarrior entity using an object. The requisiteWarrior object bundles all the essential properties and behaviors relevant to the requisiteWarrior into one package.
Gameplay is simple loop that is easy to read thanks to the requisiteWarrior object.
The game is again quite lame. No skill, no strategy. Just pure chance. But it shows how objects can simplify writing the game.

Sometimes, you need to create a bunch of objects that all have the same structure.
- You might need several monsters.
- You might need several pieces of candy.
Constructors are special functions that when invoked with the new keyword will make a new object based on a prototype template.
You might not be writing your own constructors for a while. However, most libraries and frameworks define constructors for you to use, so you must know how to use them.