Svelte store contract for all APIs of a class

MWE.svelte

<script>
  import { writable } from "svelte/store";

  class TransactionManager {
    constructor(){
      this.transactionCount = -1;
      this.transactionQueue = [];
      this._transactionIsInFlight = writable(this);
    }

    startTransaction(){
      const id = ++this.transactionCount;

      this.transactionQueue.push(id);

      console.log(`startTransaction(); Queue: ${JSON.stringify(this.transactionQueue)}`);

      this._transactionIsInFlight.set(this);
      return id;
    }

    stopTransaction(id){
      const indexOfTransaction = this.transactionQueue.findIndex(t => t === id);
      if(indexOfTransaction !== -1){
        this.transactionQueue.splice(indexOfTransaction, 1);
      }

      console.log(`endTransaction(${id}); Queue: ${JSON.stringify(this.transactionQueue)}`);
      this._transactionIsInFlight.set(this);
    }
        
    subscribe(subscriber) {
      return this._transactionIsInFlight.subscribe(subscriber);
    }
        
    transactionIsInFlight(){
      return this.transactionQueue.length > 0;
    }
  }

  const transactionManager = new TransactionManager();
  $: {
    // My aim is for this to be re-evaluated each time transactionManager.stopTransaction() is called.
    console.log("transactionIsInFlight status evaluated:", $transactionManager.transactionIsInFlight());
  }
  
  let retryTimeout;
  function retry(){
    const transactionId = transactionManager.startTransaction();
    retryTimeout = setTimeout(() => {
      transactionManager.stopTransaction(transactionId);
      retryTimeout = setTimeout(() => retry(), 1000);
    }, 1000);
  }
  retry();
</script>

<!-- My aim is for this to flip between true and false every second as transactions start and stop. -->
<p>{$transactionManager.transactionIsInFlight()}</p>