function isType(what, typeName) {
    "use strict";
    if (typeof typeName !== "string" || !typeName) {
        throw new CasperError("You must pass isType() a typeName string");
    }
    return betterTypeOf(what).toLowerCase() === typeName.toLowerCase();
}
Shorthands for checking if a value is of the given type. Can check for
arrays.

@param  mixed   what      The value to check
@param  String  typeName  The type name ("string", "number", "function", etc.)
@return Boolean