Obligation

obligation.js

var isResolvable = function (val) {
  return val && typeof val.success === 'function';
};

var reference = function (data) {
  if (isResolvable(data)) { return data; }
  return {
    success: function (callback) {
      return reference(callback(data));
    }
  };
};

var defer = function () {
  var pending = [], value;
  return {
    resolve: function (_value) {
      if (pending) {
        value = reference(_value);
        for (var i = 0; i < pending.length; i++) {
          value.success(pending[i]);
        }
        pending = void 0;
      } else {
        throw new Error('This obligation is already resolved.');
      }
    },
    success: function (_callback) {
      var result = defer();
      var callback = function (value) {
        result.resolve(_callback(value));
      };
      pending ? pending.push(callback) : value.success(callback);
      return result;
    }
  };
};

var Obligation = function () {
  return defer();
};

// Usage:
var ob = new Obligation();

// EXAMPLE 1: chain success handlers, then resolve.
ob.success(function (result) {
  console.log('In order to understand', result);
  return result;
}).success(function (result) {
  console.log('...a girl must, first, understand', result);
  return result;
});
ob.resolve('recursion');

// EXAMPLE 2: apply success handlers after resolution.
ob.resolve('be seen');
ob.success(function (result) {
  console.log('After resolution, the data may still', result);
  return result;
});