Template.chat_message.helpers({
  sender: function () {
    const me = Meteor.userId();
    let result;
    if (this.message.sender === me) {
      result = Meteor.user();
    }
    else if (this.message.sender === this.other._id) {
      result = this.other;
    }
    else {
      result = `Unknown user ${this.message.sender}.`;
    }
    return result;
  }
});