README.md

singleflight

The singleflight class is a utility that ensures only one instance of a given asynchronous operation (identified by a unique key) is executed at a time. If multiple calls are made with the same key, they will share the same promise and receive the same result instead of triggering duplicate executions.

How It Works

• The class maintains a private map (#flightsMap) that tracks ongoing asynchronous operations using unique string keys.
• The do<T>(key: string, fn: () => Promise<T>) method:
  • Checks if an operation with the given key is already running. If so, it returns the existing promise.
  • If not, it invokes the provided function (fn) and stores the resulting promise in the map.
  • Once the promise resolves or rejects, it is removed from the map to allow future executions.
• The flightsCount() method returns the current number of active asynchronous operations.

Use Case

The singleflight class is useful for preventing redundant API calls, database queries, or expensive computations when multiple requests for the same operation occur simultaneously.

Example Usage

const singleFlight = new SingleFlight();

async function fetchData(id: string) {
  return singleFlight.do(id, async () => {
    console.log(`Fetching data for ${id}...`);
    return new Promise((resolve) =>
      setTimeout(() => resolve(`Data for ${id}`), 1000)
    );
  });
}

fetchData("user-123");
fetchData("user-123"); // This call will reuse the first request instead of making a new one.