petkaantonov/bluebird · error · Error

cannot enable long stack traces after promises have been…

Error message

cannot enable long stack traces after promises have been created

    See http://goo.gl/MqrFmX

What it means

Promise.longStackTraces() can only be enabled before any promise has been created/queued, because long-stack-trace instrumentation wraps core promise methods. If async.haveItemsQueued() reports pending work and long stack traces are not yet on, Bluebird throws this Error to avoid inconsistent instrumentation.

Solutions

1. Call Promise.longStackTraces() as the very first thing after requiring bluebird, before any promise is created
2. Use the BLUEBIRD_DEBUG=1 / NODE_ENV=development environment variable which auto-enables long stack traces at load time
3. Pass longStackTraces via Promise.config({longStackTraces: true}) early at startup
4. Move the configuration out of lazy/deferred code paths to module initialization
5. Audit imports so no module creates a Bluebird promise before configuration

Example fix

// before
const app = require('./app'); // creates promises at import
Promise.longStackTraces();
// after
const Promise = require('bluebird');
Promise.longStackTraces(); // before anything else
const app = require('./app');

const Promise = require('bluebird');
if (!Promise.longStackTraces) return; // very old version
Promise.longStackTraces(); // must run before any promise creation

function canEnableLongStackTraces(Promise) {
  try { Promise.longStackTraces(); return true; }
  catch (e) { return false; }
}

try {
  Promise.longStackTraces();
} catch (e) {
  if (e.message.includes('long stack traces')) {
    console.warn('longStackTraces enabled too late; set it at startup or use BLUEBIRD_DEBUG=1');
  } else throw e;
}

When it happens

Trigger: Calling Promise.longStackTraces() (or setting config) after at least one promise has already been instantiated — e.g. enabling it inside application code that runs after module load, or in the middle of a running request handler instead of at process startup.

Common situations: Enabling longStackTraces in a middleware or lazy init path; requiring bluebird and creating promises before a config module runs; library code that creates a promise at import time, beating your configuration call.

Related errors

• cannot enable cancellation after promises are in use

AI-assisted analysis of petkaantonov/bluebird@c220cfe480 (2026-09-02). Data as JSON: /api/errors/a34fe6b345e38d2f. Report an issue: GitHub.

Appendix: source

Thrown at src/debuggability.js:144

Promise.prototype._warn = function(message, shouldUseOwnTrace, promise) {
    return warn(message, shouldUseOwnTrace, promise || this);
};

Promise.onPossiblyUnhandledRejection = function (fn) {
    var context = Promise._getContext();
    possiblyUnhandledRejection = util.contextBind(context, fn);
};

Promise.onUnhandledRejectionHandled = function (fn) {
    var context = Promise._getContext();
    unhandledRejectionHandled = util.contextBind(context, fn);
};

var disableLongStackTraces = function() {};
Promise.longStackTraces = function () {
    if (async.haveItemsQueued() && !config.longStackTraces) {
        throw new Error(LONG_STACK_TRACES_ERROR);
    }
    if (!config.longStackTraces && longStackTracesIsSupported()) {
        var Promise_captureStackTrace = Promise.prototype._captureStackTrace;
        var Promise_attachExtraTrace = Promise.prototype._attachExtraTrace;
        var Promise_dereferenceTrace = Promise.prototype._dereferenceTrace;
        config.longStackTraces = true;
        disableLongStackTraces = function() {
            if (async.haveItemsQueued() && !config.longStackTraces) {
                throw new Error(LONG_STACK_TRACES_ERROR);
            }
            Promise.prototype._captureStackTrace = Promise_captureStackTrace;
            Promise.prototype._attachExtraTrace = Promise_attachExtraTrace;
            Promise.prototype._dereferenceTrace = Promise_dereferenceTrace;
            Context.deactivateLongStackTraces();
            config.longStackTraces = false;
        };
        Promise.prototype._captureStackTrace = longStackTracesCaptureStackTrace;
        Promise.prototype._attachExtraTrace = longStackTracesAttachExtraTrace;

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