Understanding the Basic

Let's begin with understanding basic concepts of JavaScript.

Variables: number, string, boolean, null, undefined, objects.

To define a variable of any type use keyword.

var nameOfVariable = (assignment operator) Value ;

(; is must. Chrome, Firefox understand your emotions & ignores bad habit missing ; for testing purpose)

This is different from strongly-typed programming languages liked C, C++ or Java. Where the type-checking at compile time as opposed to dynamically typed languages (run-time checking) like JavaScript as shown in the above figure using Chrome V8 run-time. I would highly recommend to try this examples in your browser console.

var a = 5;

<- undefined; (return type)

Value return by run-time is of type undefined.While in-case of using operator typeof(argument)returns string "number".Declaration of a variable does not return any value that is why it returned with type undefined.Evaluated variable does not have a assigned value or defined return type; then it will return undefined.

You can override the value with any type of variable type. This seems bit odd and sounds type unsafe while working with a large code base. Usingvarkeyword again would define a new variable in the memory space. Browser gives the intellisense about available properties and methods as shown in the figure.