Returns one of the following values:

• 0 - unknown type
• 1 - double
• 2 - string
• 3 - object
• 4 - array
• 5 - buffer
• 6 - undefined
• 7 - ObjectID
• 8 - boolean
• 9 - date
• 10 - null
• 11 - regexp
• 13 - function
• 16 - integer
• 18 - long