This release introduces changes to error handling.

Previously, the parameter of the rejected promise callback was both the dispatched action and an Error object. The middleware also always constructed a new Error object, which caused unexpected mutation and circular references.

Now, the parameter of the rejected promise callback is the value of reject. The middleware does not construct a new error; it is your responsibility to make sure the promise is rejected with an Error object.

// before
const bar = () => ({
  type: 'FOO',
  payload: new Promise(() => {
    reject('foo');
  })
});.then(() => null, ({ reason, action }) => {
  console.log(action.type): // => 'FOO'
  console.log(reason.message); // => 'foo'
});

// after
const bar = () => ({
  type: 'FOO',
  payload: new Promise(() => {

    /**
     * Make sure the promise is rejected with an error. You
     * can also use `reject(new Error('foo'));`. It's a best
     * practice to reject a promise with an Error object.
     */
    throw new Error('foo');
  })
});.then(() => null, error => {
  console.log(error instanceof Error); // => true
  console.log(error.message); // => 'foo'
});