Invalid `rejected with a non-error` warning

When we set a message in out custom error object based on some non-string data, Bluebird displays Warning: a promise was rejected with a non-error: [object Object], which is clearly a mistake.

Here’s complete example:

'use strict';

var util = require('util');
var promise = require('bluebird');

function CustomError(data) {
    this.message = data;
    Error.captureStackTrace(this, CustomError);
}

util.inherits(CustomError, Error);
CustomError.prototype.name = 'CustomError';

promise.reject(new CustomError([]))
    .catch(error=> {
        console.log(error);
    });

This should not produce that warning, but it does.

[spion]

@vitaly-t Just don’t freeze the error. At the very least, leave the stack property writable, or don’t turn on longStackTraces.

By the way, I already wrote about this restriction yesterday, when you only quoted “No” from that text and LOLed. Last restriction was “the stack property needs to be writable”

https://github.com/petkaantonov/bluebird/issues/1146#issuecomment-228826885

This should definitely be in the docs, in some form.

[spion]

Remove Object.freeze(e) from lib/ext/batch.js - bluebird expects that the stack property is writable when longStackTraces are on.

(You’ll probably need to do it for lib/ext/sequence.js too, where its repeated as Object.freeze(error))

To make it easier to debug this, the freezing concern that modifies the error object should have been a part of the error unit/submodule. That way unit tests will be able to catch this.

Not sure whats going on other than that, when you run this in normal code that doesn’t attempt to do so much wrapping of bluebird behaviour

Promise.resolve()
.then(function() {
  var e = new Error();
  Object.freeze(e);
  throw e;
}).catch(function(error) {
  console.log("Caught: ", error.stack);
});

you get a clearer error:

TypeError: Cannot redefine property: stack
    at Object.defineProperty (native)
    at Object.notEnumerableProp (/node_modules/bluebird/js/release/util.js:97:9)
    at CapturedTrace.attachExtraTrace (/node_modules/bluebird/js/release/debuggability.js:725:10)
    at Promise.longStackTracesAttachExtraTrace [as _attachExtraTrace] (/node_modules/bluebird/js/release/debuggability.js:379:19)
    at Promise._rejectCallback (/node_modules/bluebird/js/release/promise.js:466:10)
    at Promise._settlePromiseFromHandler (/node_modules/bluebird/js/release/promise.js:513:17)
    at Promise._settlePromise (/node_modules/bluebird/js/release/promise.js:561:18)
    at Promise._settlePromiseCtx (/node_modules/bluebird/js/release/promise.js:598:10)
    at Async._drainQueue (/node_modules/bluebird/js/release/async.js:143:12)
    at Async._drainQueues (/node_modules/bluebird/js/release/async.js:148:10)
    at Immediate.Async.drainQueues [as _onImmediate] (/node_modules/bluebird/js/release/async.js:17:14)
    at tryOnImmediate (timers.js:543:15)
    at processImmediate [as _immediateCallback] (timers.js:523:5)