How to Determine the Type of a Message

[ballcoach12]

Given the following proto:

message UnforceValueMessage {
  required string topic   = 1; 
}
message ForceValueMessage {
  required string topic               = 1;
  required bytes data                 = 2;
  required DataMapItemType itemType   = 3;

}

I would like to use Typescript's union types in a function like this:

function publish(connection: Connection,  message: ForceValueMessage  | UnforceValueMessage){
 
if(message instanceof ForceValueMessage){
// take one action if the message is a force value
}
else if (message instanceof UnforceValueMessage){
// take another action if the message is an unforce value
}
}

The problem is that the right-hand side of the instanceof expression can't be an interface. Is there some other way that I could tell what type of message is being used here? I realize that I could either create two separate functions or adjust my proto file to return that type of the message, but I was hoping I could rely on an internal type checking mechanism in the generated code to tell me at least the string value of the type name.

Since I'm generating code from the proto file, would decorators be the way to go here? If so, do I just manually add them to the generated classes?

[jcready]

You can use the message type guards:

function publish(connection: Connection,  message: ForceValueMessage  | UnforceValueMessage){
 
if(ForceValueMessage.is(message)){
// take one action if the message is a force value
}
else {
// take another action if the message is an unforce value
}
}

Or use a proto oneof:

message UnforceValueMessage {
  required string topic   = 1; 
}
message ForceValueMessage {
  required string topic               = 1;
  required bytes data                 = 2;
  required DataMapItemType itemType   = 3;
}
message ValueMessage {
  oneof force {
    UnforceValueMessage no = 1;
    ForceValueMessage  yes = 2;
  }
}

function publish(connection: Connection,  message: ValueMessage){
 
if(message.force.oneofKind === 'yes'){
// take one action if the message is a force value
message.force.yes.data;
}
else if (message.force.oneofKind === 'no'){
// take another action if the message is an unforce value
message.force.no.topic;
}
}

[ballcoach12]

Wow! Thanks! I somehow missed that in the docs (I guess reading is helpful!)