21 lines of explanation for a change that amounted to swapping the arguments to a `||`.

fixed.js

const errorMessage = this.state.errorMessage || (this.props.error && this.props.error.message);

original.js

const errorMessage = (this.props.error && this.props.error.message) || this.state.errorMessage;

sweet-comment.js

    // Show our internal error message before showing any error that may have
    // come from the outside, because the internal error message is generated
    // before any external one could have been.  When we prioritize the external
    // error message, the following flow results in the wrong message being
    // displayed:
    //   1. User enters a card that will be declined by the server
    //      (try "4000000000000002")
    //   2. "Your card has been declined" error is displayed (external)
    //   3. The user then enters a card that will be declined by the client,
    //      which is an internal error generated by the Stripe.js client in the
    //      call to createToken.
    //      (try "4242424242424241" or try using only a 2 digit CVC)
    //   4. The same "Your card has been declined" error is still displayed even
    //      though it is no longer valid.
    // This happens because the external error is not cleared when the form is
    // resubmitted, because the first acts internal to this
    // component, instead of being externalized in a Flux action.
    //
    // With this fix in, there is still an annoying flash of the prior error
    // message, but it is at least better to have the most accurate error
    // message displayed when the action is completed.