I have 2 services, each has its own transaction block like this:

function tranA() {
    const session = await this.connection.startSession();
    try {
        session.startTransaction();

        // Query with the session

        await session.commitTransaction();
    } catch {
        await session.abortTransaction();
    } finally {
        await session.endSession();
    }
}

In one controller, I have to call these 2 services, and make sure that they use
the same transaction i.e. same session. How should I approach this?

My only idea so far is to move the queries into separate functions, then pass
the session down, like this:

function tranA() {
    const session = await this.connection.startSession();
    try {
        session.startTransaction();

        this.A(session)

        await session.commitTransaction();
    } ...
}

function A(session) {
    // Query with the session
}

then in the controller, I create my own session then call the services.

The biggest problem with this approach is the duplication of method names. Now
many methods will have 2 versions, one with external session, one with its own
session.