Provide .done() or other method to throw Exception out of chain

[ivan-kleshnin]

Consider this code:

// fragment of react-based app

Axios.get('/api/robots/')
  .then((res) => { // could be .done() if... see below
    let self = this;
    //setTimeout(function() { // -- this is ugly disabled workaround --
      self.setState(res.data); // if error happen here
    //}, 1);
    console.log(">>> RobotStore.state:", this.state);
  })
  .catch((res) => {
    if (res instanceof Error) { // it is catched here
      // unpredictable error, release 
      throw Error("test"); // this DOES NOT work, error is swallowed (reject promise which is never used)
    } else {
      // HTTP error, handle
      this.setState(this.getInitialState());
    }
  }); 

So axios (actually ES6 Promise engine) swallows app errors (which I want to bubble up and crash everything, as it's not runtime error).

http://bahmutov.calepin.co/why-promises-need-to-be-done.html

But looks like done still is not a part of spec and "ugly workaround" is required. Some authors insist on deprecating done at all.

http://stackoverflow.com/questions/26667598/will-javascript-es6-promise-support-done-api

I'ml aware of all aspects of this subject. What can you propose to solve this issue?
Monkeypatch .done? Leave setTimeout "trick" as it is? Or there are other ways?

[mzabriskie]

I am really frustrated with ES6 Promises. I was unfortunately unaware of the error swallowing behavior when I first started with axios, and thought that building on standardized, native Promises was the right thing. I am questioning that decision now.

I have thought a lot about what should be done, and have ultimately concluded that axios itself won't do anything to try and solve the problem. Instead I will let consumers decide how they want to handle it. Long term, browser dev tools should report an error when the Promise is garbage collected.

Until then I personally would consider using a polyfill for done, such as https://www.promisejs.org/polyfills/promise-done-6.1.0.js. I think that it's cleaner than doing the setTimeout yourself.

[ivan-kleshnin]

@mzabriskie, thank you for this comprehensive answer!
I actually agree with your advice, and already made the same choice of polyfilling.