singleflight

Single flight pattern for TypeScript, deduplicate concurrent requests.

installation

yarn add @jswork/singleflight

usage

import SingleFlight from '@jswork/singleflight';

const sf = new SingleFlight<string>();

// Concurrent dedup: same key executes only once
const result = await sf.run('user:1', () => fetch('/api/user/1').then(r => r.json()));

real-world example: token refresh

When multiple requests hit a 401 at the same time, you only want one refresh call — the rest share the same Promise.

import SingleFlight from '@jswork/singleflight';

const sf = new SingleFlight<string>();
let token = '';

async function refreshToken(): Promise<string> {
  return sf.run('refresh-token', async () => {
    const res = await fetch('/api/refresh-token', {
      method: 'POST',
      headers: { Authorization: `Bearer ${token}` },
    });
    const data = await res.json();
    token = data.token;
    return token;
  });
}

async function request(url: string, options?: RequestInit) {
  const res = await fetch(url, {
    ...options,
    headers: { ...options?.headers, Authorization: `Bearer ${token}` },
  });

  if (res.status === 401) {
    const newToken = await refreshToken();
    return fetch(url, {
      ...options,
      headers: { ...options?.headers, Authorization: `Bearer ${newToken}` },
    });
  }

  return res;
}

license

Code released under the MIT license.