Generates a sequence of thens

promise-thenseq.js

// Requires https://github.com/tildeio/rsvp.js

// Once in a blue moon we need to concatenate several thens executing basically the same code.
// Example:
// f().then(function(message) {
//   alert(message + " #1");
//   return f();
// }).then(function(message) {
//   alert(message + " #2");
//   return f();
// }).then(function(message) {
//   alert(message + " #3");
//   return f();
// }).then(function(message) {
//   alert("last call");
// }, function(error) { // handle error });
// The following function let us compact the previous example, producing a sequence of thens sharing a common iterator.
// Example:
// f().sequence(1, 3, function(message, iter) {
//   alert(message + " #" + iter);
// }).then(function() {
//  alert("last call");
// }, function(error) { // handle error });
RSVP.Promise.prototype.sequence = function(start, end, fulfilled) {
  var promise = this;
  var shared = {iter: start};
  for (var j=start; j<=end; j++) {
    var wrapper = function() {
      var args = Array.prototype.slice.call(arguments);
      if (args.length == 1 && 'undefined' == typeof(args[0])) { args = [] };
      var i = this.iter;
      this.iter++;
      return fulfilled.apply(this, args.concat(i));
    }
    promise = promise.then(wrapper.bind(shared));
  }
  return promise;
}