Is such an expression valid for Mongo Db?

Question

MongoDB

Good afternoon, is such an expression valid for inserting an element into a database with variable values ​​of the chat array (activeChat) and the messages object (msg) for Mongo Db?

this.db.chat.update({
        $let: {
          vars: {updchat: activeChat, updmessage: msg},
          in: {$push: ["$$updchat", "$$updmessage"]}
        }
      })