Long Stack Support for ES6 Promises.js

'use strict';

const theGlobal = typeof window === 'object' ? window : global;

const realPromiseConstructor = theGlobal.Promise;

const wrappedPromiseConstructor = function (resolve, reject, progress) {
    const originalPromiseInstance = new realPromiseConstructor(resolve, reject, progress);
    
    // Who called us?  Let's store it.
    const stackWhenCalled = new Error().stack;
    
    const wrappedPromiseInstance = originalPromiseInstance.catch((err) => {
        try {
            err.stack = err.stack || '';
            err.stack += '\nDuring promise started:\n' + stackWhenCalled.split('\n').slice(3).join('\n');
        } catch (err2) {
            console.error("promiseDebugging.reportLongStackTraces had difficulty adding to the stack:", err2);
        }
        return realPromiseConstructor.reject(err);
    });
    
    return wrappedPromiseInstance;
};
Object.setPrototypeOf(wrappedPromiseConstructor, realPromiseConstructor);

theGlobal.Promise = wrappedPromiseConstructor;

I find this pretty useful, but NodeJS developers might find the longjohn module even more useful, because it can track long stacktraces through callbacks as well as through promises. As a result, it also works when your app and its dependencies are using different promise libraries.

I sometimes add clarify too (and tweak it a little) to remove some of the uninteresting lines from the stacktrace.

Update: This package trace-and-clarify-if-possible looks promising

This one just saved my life!

Unfortunately, this trick does not work with native async-await, because the engine doesn't call our global promise constructor.

But it does work with transpiled async-await.

NodeJS now does this out of the box, since --async-stack-traces has been enabled by default.