node:async_hooks

The node:async_hooks module in Azion Runtime: AsyncLocalStorage and AsyncResource inside a function, and a sample that carries a request ID.

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The node:async_hooks module tracks the lifecycle of asynchronous resources, as the Node.js async_hooks documentation describes. Its hooks fire at each stage of an asynchronous operation, for context propagation and debugging. In Azion Runtime, the module is available through Node.js compatibility. Its common use in a function is AsyncLocalStorage, which carries request-scoped data, such as a request ID, across asynchronous calls.

In a deployed function and under azion dev, AsyncLocalStorage keeps its store across an await and into a setTimeout callback, and outside run(), getStore() returns no value. AsyncResource works too: runInAsyncScope() runs its callback and returns the callback’s value.

Example

The function below reads the X-Request-Id header, stores it with AsyncLocalStorage, and logs it from functions that do not receive it as an argument:

JavaScript
01/**
02 * An example of using the Node.js Async Hooks API in an Azion Function.
03 * @example
04 * // Build and run locally with the Azion CLI:
05 * azion build
06 * azion dev
07 */
08import { AsyncLocalStorage } from "node:async_hooks";
09
10const requestId = new AsyncLocalStorage();
11
12function logAsyncContext(state) {
13 console.log(`${requestId.getStore()} - ${state}`);
14}
15
16function doSomething() {
17 logAsyncContext("log from sync function");
18 setTimeout(() => doSomethingElse(), 100);
19}
20
21function doSomethingElse() {
22 logAsyncContext("log from setTimeout callback");
23}
24
25/**
26 * Example of using the Node.js Async Hooks API
27 * @param {*} event
28 * @returns {Promise<Response>}
29 */
30async function main(event) {
31 const id = event.request.headers.get("X-Request-Id") ?? "unknown";
32
33 return requestId.run(id, () => {
34 doSomething();
35 logAsyncContext("log from another sync function");
36 return new Response("ok");
37 });
38}
39
40export default main;

A request with the header X-Request-Id: req-1 receives the body ok. While the request runs, the function logs these lines:

Text
01req-1 - log from sync function
02req-1 - log from another sync function
Node.js APIs

Every Node.js module Azion Runtime resolves, and how each one behaves.

node:timers

The timer functions, such as the setTimeout call this sample schedules.

Use Node.js APIs through polyfills

How the build resolves Node.js APIs through polyfills, shown in a JavaScript project.

Handlers

The recommended handler shape, and the notice azion build prints for the export default main shape this sample uses.