proto buf

	message Customer {

		enum Type {
				REGULAR = 0;
				MEMBER = 1;
				SPONSOR = 2;
		}

		Type type = 1;

	}

optional int32 results_per_page = 1 [default = 25];

no default value, always zero value

protoc --js_out=import_style=commonjs, binary:. messages.proto

oneof access_type {
	string email = 1;
	string username = 2;
}

oneof  

- only one field can hold value
- setting one field clears others

maps

message Customer {
	map<string, string> email_addresses = 1;

	// keys must be strings or integer types
}

any

import "google/protobuf/any.proto";

message Customer {
	int32 id = 1;
	string username = 2;
	repeated google.protobuf.Any details = 3;	
}

reserved 1;
reserved 1,2,3;
reserved 5 to 10;
reserved 2, 4, 15 to 25;