snippet.js

    // Given a function that accepts a callback with the functions response
    // executes the function waiting for the callback, and setting `content`
    // to the returned value before preceeding to the next item in the queue.
    async: function(fun, callback) {
      return this.then(function(content) {
        var context = this;
        this.wait();
        fun(function(response) {
          context.next(response);
        });
        return false;
      }).then(callback);
    }