Blocking Call In Async (ARCH3028)

Key typescript.async.blocking-call-in-async · Severity error · Category async

Synchronous blocking calls (sleep, blocking IO, blocking HTTP/DB drivers) inside an async function stall the event loop and starve concurrency.

Incorrect

import { readFileSync } from "fs";

async function loadTemplate(path: string): Promise<string> {
  return readFileSync(path, "utf8"); // blocks the event loop
}

Correct

import { readFile } from "fs/promises";

async function loadTemplate(path: string): Promise<string> {
  return await readFile(path, "utf8");
}

Fix

Replace the synchronous blocking call with its asynchronous, awaitable counterpart.