@hoangsonw/fast-fetch/src/fastFetch.ts

A smarter fetch() wrapper with auto-retry, deduplication, and minimal boilerplate.

import fetch from "cross-fetch";

/**
 * Options for controlling FastFetch behavior:
 * - `retries` -> number of times to retry on failure
 * - `retryDelay` -> base delay in ms before next retry (will be multiplied exponentially)
 * - `deduplicate` -> whether to merge identical requests in-flight
 * - `shouldRetry` -> custom logic to decide if we retry
 */
export interface FastFetchOptions {
  retries?: number;
  retryDelay?: number;
  deduplicate?: boolean;
  shouldRetry?: (error: any, attempt: number) => boolean;
}

/**
 * Ongoing in-flight requests for deduplication:
 * Keyed by a stable signature of { url, method, headers, body }
 */
const inFlightMap = new Map<string, Promise<Response>>();

/**
 * Generate a signature for dedup if deduplicate is true
 */
function makeSignature(input: RequestInfo, init?: RequestInit): string {
  // Basic approach:
  const normalized = {
    url: typeof input === "string" ? input : (input as Request).url,
    method: init?.method ?? "GET",
    headers: init?.headers ?? {},
    body: init?.body ?? null,
  };
  return JSON.stringify(normalized);
}

/**
 * Sleep helper for retryDelay
 */
function sleep(ms: number) {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

/**
 * FastFetch main function
 * - Retries on error with exponential backoff
 * - Deduplicates in-flight requests if deduplicate = true
 */
export async function fastFetch(
  input: RequestInfo,
  init?: RequestInit & FastFetchOptions,
): Promise<Response> {
  const {
    retries = 0,
    retryDelay = 1000,
    deduplicate = true,
    shouldRetry,
  } = init || {};

  console.log("[FastFetch] Starting request for:", input);

  // If deduplicating, check if a matching in-flight request exists
  let signature = "";
  if (deduplicate) {
    signature = makeSignature(input, init);
    if (inFlightMap.has(signature)) {
      console.log(
        "[FastFetch] Found in-flight request for signature:",
        signature,
      );
      return inFlightMap.get(signature)!;
    }
  }

  // Build a promise chain that tries up to retries + 1 times with exponential backoff
  let attempt = 0;
  let promise = (async function fetchWithRetry(): Promise<Response> {
    while (true) {
      try {
        attempt++;
        console.log(`[FastFetch] Attempt #${attempt} for:`, input);
        const response = await fetch(input, init);
        if (!response.ok && shouldRetry) {
          const doRetry = shouldRetry(response, attempt);
          console.log(
            `[FastFetch] Response not ok (status: ${response.status}). Retry decision: ${doRetry}`,
          );
          if (doRetry && attempt <= retries) {
            const delay = retryDelay * Math.pow(2, attempt - 1);
            console.log(
              `[FastFetch] Waiting ${delay}ms (exponential backoff) before retrying...`,
            );
            await sleep(delay);
            continue; // try again
          }
        }
        console.log(`[FastFetch] Request succeeded on attempt #${attempt}`);
        return response;
      } catch (error: any) {
        console.log(`[FastFetch] Caught error on attempt #${attempt}:`, error);
        if (shouldRetry) {
          const doRetry = shouldRetry(error, attempt);
          console.log(`[FastFetch] Retry decision based on error: ${doRetry}`);
          if (doRetry && attempt <= retries) {
            const delay = retryDelay * Math.pow(2, attempt - 1);
            console.log(
              `[FastFetch] Waiting ${delay}ms (exponential backoff) before retrying after error...`,
            );
            await sleep(delay);
            continue;
          }
        } else {
          if (attempt <= retries) {
            const delay = retryDelay * Math.pow(2, attempt - 1);
            console.log(
              `[FastFetch] Retrying attempt #${attempt} after error. Waiting ${delay}ms...`,
            );
            await sleep(delay);
            continue;
          }
        }
        console.log("[FastFetch] No more retries. Throwing error.");
        throw error;
      }
    }
  })();

  // If deduplicating, store in the map so subsequent calls get the same promise
  if (deduplicate) {
    inFlightMap.set(signature, promise);
    console.log(
      "[FastFetch] Stored in-flight request with signature:",
      signature,
    );
  }

  try {
    const result = await promise;
    return result;
  } finally {
    // Once done (success or fail), remove from inFlightMap
    if (deduplicate) {
      inFlightMap.delete(signature);
      console.log(
        "[FastFetch] Removed in-flight record for signature:",
        signature,
      );
    }
  }
}