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NaN: Not a number: As the name implies, it is used to denote that the value
of an object is not a number. There are many ways that you can generate
this error, one being invalid math opertaions such as 0/0 or sqrt(-1)
undefined: It means that the object does not have any value, therefore
undefined. This occurs when you create a variable and don't
assign a value to it.
null: It means that the object is empty and is not pointing to any memory
address.