Add Symbol.toStringTag to promise instance

[Strate]

As for now, promise created by Bluebird does not have Symbol.toStringTag, but have toString method which returns "[object Promise]" string. Having [Symbol.toStringTag]: "Promise" make Object.prototype.toString.call(promise) to return same string: "[object Promise]" (as for now it will return "[object Object]" string.
So, I suggest to add Symbol.toStringTag property to bluebird's promise prototype.

[benjamingr]

I don't know how I feel about this. How would users be able to tell native promises apart?

[ronzeidman]

import * as Bluebird from 'bluebird';
console.log(Promise.toString().includes('[native code]')); //true
const NativePromise = global.Promise;
global.Promise = Bluebird;
console.log(Promise.toString().includes('[native code]')); //false
const a = Promise.resolve();
console.log(a instanceof NativePromise); //false
console.log(a instanceof Promise); //true


function isNativePromise(promise: Promise<any>) {
    return promise.constructor.toString().includes('[native code]');
}

[torkelrogstad]

The fact that Bluebird promises and native ES6 promises are incompatible makes it very difficult to work with packages like Sequelize in TypeScript. Please consider implementing this change.

[benjamingr]

I don't understand why you think bluebird is incompatible with native promises in TypeScript - I've been happily using them together for quite a while. That fact is unrelated to how toStringTag behaves.

[spion]

They cannot be passed where a native promise is required as an argument due to the missing toStringTag symbol.

[spion]

Theoretically, the .d.ts file could contain it -- however, DT maintainers are reluctant to add something that does not exist (and with good reason):

DefinitelyTyped/DefinitelyTyped#11027 (comment)

[spion]

We should definitely do this, the only questions are:

• can we make it so that Object.prototype.toString.call(promise) returns the same thing it did before
• is anyone using the presence of [Symbol.toStringTag] directly to tell native from BB promises apart.