reactivex_player_callback_hell.js

function play(movieId, cancelButton, callback) {
    var movieTicket,
        playError,
        tryFinish = function () {
            if (playError) {
                callback(null, playError);
            }
            else if (movieTicket && player.initialized) {
                callback(null, ticket);
            }
        };

    cancelButton.addEventListener("click", function () { playError = "cancel"; });

    if (!player.initialized) {
        player.init(function () {
            playError = error;
            tryFinish();
        });
    }

    authorizeMovie(movieId, function (error, ticket) {
        playError = error;
        movieTicket = ticket;
        tryFinish();
    });

}