[node.js] count active promises via the V8 inspector

count-promises.js

"use strict"
const inspector = require("node:inspector/promises")
const session = new inspector.Session()
session.connect()
countPromises(session).then(console.log)

async function countPromises(session) {
    // resource management: put all results in an object group
    const objectGroup = crypto.randomUUID()

    // get reference to global Promise object prototype
    const {result:{objectId:promisePrototypeOID}} = await session.post(
        "Runtime.evaluate",
        {objectGroup, expression:"Promise.prototype"})

    // get reference to array holding all promises
    const {objects:{objectId:promisesArrayOID}} = await session.post(
        "Runtime.queryObjects",
        {objectGroup, prototypeObjectId:promisePrototypeOID})

    // get contents of array; disable preview for performance reasons
    const {result} = await session.post(
        "Runtime.getProperties",
        {objectId:promisesArrayOID, ownProperties:true, generatePreview:false})

    // free resources, don't wait for completion
    session.post("Runtime.releaseObjectGroup", {objectGroup})

    // array includes "length" property, subtract one to correct
    return result.length - 1
}