Cancelling Operations with AbortController

AbortController creates a signal that cooperative APIs can use to stop pending work. Aborting does not roll back a completed side effect, and an API must support the signal for cancellation to work. fetch can receive the signal via its options.

Reading the code: The controller is aborted before fetch begins, so fetch rejects for the aborted signal. The catch block identifies the error name AbortError. No network request is needed.

Keep the boundary clear: Aborting a request does not guarantee that a server operation was undone; design idempotent or safely retryable server actions separately.

Save the code as cancelling-operations-abortcontroller.ts. The result below was captured after compiling this exact example with strict TypeScript checking and executing the emitted JavaScript in Node.js.

TypeScript code

async function main(): Promise<void> {
  const controller = new AbortController();
  controller.abort();
  try {
    await fetch("data:text/plain,hello", { signal: controller.signal });
  } catch (error: unknown) {
    if (error instanceof Error) console.log(error.name);
  }
}
main().catch(console.error);

Verified output

AbortError

Build: npx tsc --strict --target es2022 --module commonjs --lib es2022,dom,esnext.disposable cancelling-operations-abortcontroller.ts; run: node cancelling-operations-abortcontroller.js. The exact filename may be changed freely. When a multi-file project exists, prefer its tsconfig.json and build scripts.

The controller is aborted before fetch begins, so fetch rejects for the aborted signal. The catch block identifies the error name AbortError. No network request is needed.

The output shown above comes from the initialized values in this program. Replacing a type annotation alone does not transform a JavaScript value.

Aborting a request does not guarantee that a server operation was undone; design idempotent or safely retryable server actions separately.

Check both the TypeScript diagnostic and the emitted JavaScript behavior. A program can compile correctly and still need runtime validation or error handling.

Create a controller, pass its signal to an operation, and trigger abort from a timeout, clearing the timeout when work finishes.

Before running your change, write down the type you expect TypeScript to infer and the output you expect JavaScript to print. Then check both predictions.

AbortController creates a signal that cooperative APIs can use to stop pending work.

Try the practice change and re-run the exact program to test your understanding.