Instrumentation hooks

Tap into console, fetch, XMLHttpRequest, clicks and uncaught errors — for a monitoring backend, a debug overlay, or tests.

Every one of them returns a teardown function. Keep it and call it. Instrumenting a global without a way back is a one-way door: tests cannot clean up after themselves, and a hot reload re-patches an already-patched global until each call is nested through a dozen wrappers and every event is reported N times.

API

Function	Instruments	Returns
handleConsole(hook)	console.log/info/warn/error/assert	restore
handleFetchHook(options)	window.fetch	restore
handleXhrHook(options)	XMLHttpRequest#open / #send	restore
handleError(hook)	error + unhandledrejection	unsubscribe
handleClick(hook)	document clicks (capture phase)	unsubscribe
replaceOld(obj, key, wrap)	any property on any object	restore

handleFetchHook / handleXhrHook take { requestHook, responseHook, errorHook }.

Example

import { handleConsole, handleError, handleFetchHook } from 'ranuts';

const teardown = [
  handleConsole((type, ...args) => send({ type, args })),
  handleError((error) => send({ type: 'error', error: String(error) })),
  handleFetchHook({ errorHook: (url, error) => send({ type: 'fetchError', url }) }),
];

// on teardown (HMR, route change, test cleanup)
teardown.forEach((off) => off());

Notes

1. Original behaviour is preserved. Responses pass through, errors are re-thrown, console output still prints.
2. replaceOld's restore only undoes its own patch. If another layer patched on top afterwards, restoring blindly would silently uninstall that layer, so it declines instead.
3. handleXhrHook patches the prototype, so it applies to every instance; its listeners are registered with { once: true } so a reused XHR object does not accumulate them.
4. Do not report console output to a console-logging backend — the hook fires on the very call it produces. (This is why Monitor's console channel is off by default.)

Changed in 0.3

These all used to return void, with no way to uninstall. They now return a teardown function; existing call sites keep working and can simply start using it.