Typeof

The typeof operator returns the data type of the parameter, but it has various 'gotchas'.

Things to be aware of:

typeof recognizes NaN as a number.
typeof recognizes any complex data types, like Arrays or Maps, as simply object.
typeof also recognizes null as an object.
There are better ways to determine the types of complex data objects. For arrays, you can call Array.isArray(object) method. Other data types have similar methods for determining type.