Async Local Context

async-local-context.js

// Async Local Context

// Requires Node.js nightly features and fixes, planned (I believe) to be released in 8.2.0

// Call `createContext()` to create a new local context.
// Call `getContext()` anywhere under that to retrieve the same local context.
// Call `createContext()` when there is already an existing context to create a new child context which inherits from the parent.

import { createHook, executionAsyncId } from 'async_hooks'

let contexts = new Map()

createHook({
	init(asyncId, type, triggerAsyncId) {
		contexts.set(asyncId, contexts.get(triggerAsyncId))
	},
	destroy(asyncId) {
		contexts.delete(asyncId)
	},
}).enable()

export function createContext() {
	contexts.set(executionAsyncId(), Object.create(getContext() || null))
}

export function getContext() {
	return contexts.get(executionAsyncId())
}