typescript class with static variable / singleton pattern

Question

well i have a question regarding the best way to code this situation: i have a class where i need to have a static variable in all the project: connection

singleton without name space:

class Broker {
  static connection: Connection = undefined;
  static channel: Channel = undefined;
  static urli: string = process.env.RABBIT_URL || 'url';
  static start() {
    return new Promise<Connection>((resolve, reject) => {
      if (Broker.connection || !Broker.urli) {
        const message = !Broker.urli
          ? 'The host of rabbitmq was not found in the environment variables'
          : 'Connection has already been established';
        logger.info(message);
        reject(new Error(message));
      }
      retry<Connection>(() => connect(Broker.urli), 10, 1000)
        .then((conn) => {
          Broker.connection = conn;
          resolve(conn);
        })
        .catch((err) => reject(new Error(err)));
    });
  }
}
export const ConnectionMQ: Connection = Broker.connection;
export const ChannelMQ: Channel = Broker.channel;
export const start = () => {
  return Broker.start();
};

with namespace

//namespace
namespace Broker {
  export type QueuesToAssert = { queue: string; options?: Options.AssertQueue };
  export type ExchangesToAssert = {
    exchange: string;
    type: string;
    options?: Options.AssertExchange;
  };
  export type QueuesToBind = {
    queue: string;
    source: string;
    pattern: string;
    args?: any;
  };
  //static
  class BrokerMain {
    static connection: Connection = undefined;
    static channel: Channel = undefined;
    static urli: string = process.env.RABBIT_URL || 'url';
    static start() {
      return new Promise<Connection>((resolve, reject) => {
        if (BrokerMain.connection || !BrokerMain.urli) {
          const message = !BrokerMain.urli
            ? 'The host of rabbitmq was not found in the environment variables'
            : 'Connection has already been established';
          logger.info(message);
          reject(new Error(message));
        }
        retry<Connection>(() => connect(BrokerMain.urli), 10, 1000)
          .then((conn) => {
            this.connection = conn;
            resolve(conn);
          })
          .catch((err) => reject(new Error(err)));
      });
    }
  }
  export const Connection = BrokerMain.connection;
  export const Channel = BrokerMain.channel;
  export const start = () => {
    return BrokerMain.start();
  };
  export const close = () => {};
}
//usage
const connection = Broker.Connection ? Broker.start() : undefined;

I would like to know what is the best / correct option in this situation, or if I could apply another way to the situation. remembering that I only need 2 unique variables of the class that are unique statics throughout the project. I have doubts if the singleton is needed in this case or just static already solves

Neither is appropriate. Use modules. Basically, remove the namespace Broker {} wrapper from the namespace example and he happy — Aluan Haddad
– Aluan Haddad, Commented Sep 9, 2020 at 23:51
but that way will my connection from the class Broker have a static value throughout the project? — Ming
– Ming, Commented Sep 9, 2020 at 23:53
Of course. But you would do export let Connection: Connection; then change this.connection = conn to Connection = conn. That will fix an existing bug and simply your code — Aluan Haddad
– Aluan Haddad, Commented Sep 10, 2020 at 0:03
I edited the code based on that, could you tell me if this is it? the first code block — Ming
– Ming, Commented Sep 10, 2020 at 0:14
That's very close to what I meant but if you look at my last comment, you need to use export let for the connection and you need set it when you get the connection in your call back. The problem with your current implementation is that the value never gets updated. export const ConnectionMQ: Connection = Broker.connection will always be undefined. — Aluan Haddad
– Aluan Haddad, Commented Sep 10, 2020 at 0:22

basarat · Accepted Answer · 2020-09-09 23:45:19Z

1

I would like to know what is the best / correct option in this situation,

I would definitely recommend the static class methods.

Reason

namespace is a TypeScript only feature and not supported by many tools out of the box e.g. Create React App.

answered Sep 9, 2020 at 23:45

basarat

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2 Comments

Ming Over a year ago

basarat and in this situation where I said that I only need 2 static variables: connection and channel, that is, just one value in the entire project, would I need to use singleton for this? or just declaring the variable as static would solve it already?

basarat Over a year ago

A static is a singleton 👍

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