cnysa

cnysa (unpronouncible) is a module that allows you to see information about what the async_hooks module is doing under the covers.

Usage

Require cynsa in your application:

node --require cynsa app.js

Understanding output

For each init, before, promiseResolve, and destroy event, a line will be printed.

Each of those lines start with a symbol:

• + Init
• * Before
• - Destroy
• : Promise Fulfillment

The number that follows is the current time in seconds, mod 1000.

A string after represents the async resource type.

After that, you get a list of numbers delimited by :. The first number is the uid passed in to the corresponding hook, and subsequent numbers follow its triggerAsyncId chain.

For before lines, you'll also see the current execution ID (ex), trigger ID (tr), and an opening brace.

before-after pairs are visualized as indents. A closing brace indicates an after event emission.

Example

Let's say the following is app.js:

const express = require('express');

const server = express()
  .get('/', (req, res) => res.send("i'm rooting for you"))
  .listen(8080);
setTimeout(() => server.close(), 5000);

Running the command in the "Usage" section gives you (in colors):

+ [  0] TCPWRAP 6:1
+ [  0] TickObject 7:6:1
+ [  0] Timeout 8:1
+ [  0] TIMERWRAP 9:1
* [  0] TickObject 7|ex 7|tr 6 {
}
- [  0] TickObject 7
* [  5] TIMERWRAP 9|ex 0|tr 0 {
  * [  5] Timeout 8|ex 8|tr 1 {
    + [  5] TickObject 10:8:1
  }
}
* [  5] TickObject 10|ex 10|tr 8 {
}
- [  5] Timeout 8
- [  5] TickObject 10
- [  5] TIMERWRAP 9
- [  5] TCPWRAP 6