JavaScript Variables and Arrays

JavaScript Variables
Variables are used to hold data in memory. JavaScript variables are declared with the var keyword.
var age;
Multiple variables can be declared in a single step.
var age, height, weight, gender;
After a variable is declared, it can be assigned a value.
age = 34;
Variable declaration and assignment can be done in a single step.
var age = 34;
A Loosely-typed Language
JavaScript is a loosely-typed language. This means that you do not specify the data type of a variable when declaring it. It also means that a single variable can hold different data types at different times and that JavaScript can change the variable type on the fly. For example, the age variable above is an integer. However, the variable strAge below would be a string (text) because of the quotes.
var strAge = "34";
If you were to try to do a math function on strAge (e.g, multiply it by 4), JavaScript would dynamically change it to an integer. Although this is very convenient, it can also cause unexpected results, so be careful.
Arrays
An array is a grouping of objects that can be accessed through subscripts. At its simplest, an array can be thought of as a list. In JavaScript, the first element of an array is considered to be at position zero (0), the second element at position one (1), and so on. Arrays are useful for storing data of similar types.
Arrays are declared using the new keyword.
var myarray = new Array();
It is also possible and very common to use the [] literal to declare a new Array object.
var myarray = [];
Values are assigned to arrays as follows.
myarray[0] = value1;
myarray[1] = value2;
myarray[2] = value3;
Arrays can be declared with initial values.
var myarray = new Array(value1, value2, value3);
//or, using the [] notation:
var myarray = [value1, value2, value3];