Generating map<K, V> on javascript type issue

What version of protobuf and what language are you using?
Version: master/v3.18
Language: Javascript

What operating system (Linux, Windows, ...) and version? Linux

What runtime / compiler are you using (e.g., python version or gcc version) Nodejs

What did you do?
Steps to reproduce the behavior:

1. Trying to export type map<K, V> so I created a proto file like this:

message MessageResponse {
  string _id = 1;
  string title = 2;
  bool disabled = 3;
  map<string,string> metadata = 4;
}

2. Converting it using this some commands like this:

protoc -I=/libraries/protos/ /libraries/protos/src/*.proto /libraries/protos/src/**/*.proto --plugin=/libraries/protos/binaries/linux/protoc-gen-grpc-web --js_out=import_style=commonjs,binary:/libraries/protos/build/typescript --grpc-web_out=import_style=typescript,mode=grpcwebtext:/libraries/protos/build/typescript --experimental_allow_proto3_optional

3. What I am getting on .ts files is something like:

export namespace MessageResponse {
  export type AsObject = {
    id: string,
    title: string,
    disabled: boolean,
    metadataMap: Array<[string, string]>,
  }
}

4. Well we can see there is a suffix called Map added to my field name! also the generated type is Array<[string, string]>. but what we were expecting, based on language guide here, where an object of {"k": v, …}, like Record<string, V>

What did you expect to see
An object like: Record<string, string>

What did you see instead?
Array<[string, string]>

Begin with the provided .proto map field and protoc command, then inspect the generated MessageResponse .ts AsObject declaration. Reproduce the output with the stated master/v3.18 and Node.js setup; done when the generated map type and field naming match the documented JavaScript/TypeScript expectation.