Observer like object to maintain a reference to data that can or will change a lot.

Objserver.js

    /**
    Creates a new Objserver.
    @class Observes an object and updates its value on changes that are applied.
    @param [value] - Optional init value; - 
    */ 
    function Objserver(value) {
      this.$value = value;
      this.$change = [];
    }
    function jsonPath(obj,string) {
      var parts = string
          .replace(/\[/g, '.')
          .replace(/\]/g, '')
          .split("."),
        path = obj;
      parts.forEach(function(part){
        path = path[part];
      });
      return path;
    }
    /**
     * @memberOf Objserver
     * Adds a change listener that is fired if somthing changes
     * @returns {Objserver} self - For chaining
     */
    Objserver.prototype.onChange = function(cb) {
      this.$change.push(cb);
      return this;
    };
    /**
     * @memberOf Objserver
     * @param {function} listener - Listener to remove.
     * @returns {Objserver} self - For chaining
     */
    Objserver.prototype.off = function(cb) {
      this.$change.splice(this.$change.indexOf(cb), 1);
      return this;
    };
    /**
     * Trigger change event
     * @memberOf Objserver
     * @param newval - The new value
     * @param newval - The old value
     * @returns {Objserver} self - For chaining
     */
    Objserver.prototype.change = function(newval, oldval) {
      var _self = this;
      this.$change.forEach(function(fn, index) {
        var $event = {
          class : Objserver,
          instance  : _self,
          value : _self.$value
        };
        fn.call($event, newval, oldval);
      });
      return this;
    };
     /**
     * Get current value
     * @memberOf Objserver
     * @returns value current value
     */
    Objserver.prototype.val = function() {
      return this.$value;
    }
    /**
     * Bind the value to some object to keep that object informed on updates.
     * @memberOf Objserver
     * @param {object} object - Object to bind to
     * @param {string} name - Attribute name
     * @returns {Objserver} self - For chaining
     */
    Objserver.prototype.bind = function(object, name) {
      object[name] = this.$value;
      this.change(function(value) {
        object[name] = value;
      });
      return this;
    };
    /**
     * Maps function on object, native map fo arrays or unboxing for promises
     * @memberOf Objserver
     * @param {function} fn - The function to map.
     * @returns {Objserver} self - For chaining
     */
    Objserver.prototype.map = function(fn) {
      var _self = this;
      if(this.$value.then) {
        _self.$value.then(function(value) {
          _self.ap(fn);
        })
      }
      var newVal = this.$value.map(fn), oldVal = this.$value;
      this.$value = newVal;
      this.change(newVal, oldVal);
      return this;
    };
    /**
     * Map / Apply method
     * @memberOf Objserver
     * @param {function|Promise|object} cb - The Object/Promise or function to apply.
     * @param {string} jsonpath - the path to the value you supplied.
     * @returns {Objserver} self - For chaining
     */
    Objserver.prototype.ap = function(cb,jsonpath) {
      var _self = this,
          oldVal,
          newVal;
      if(this.$value && this.$value.then) {
        _self.$value.then(function(value) {
          _self.$value = value;
          _self.ap(cb);
        });
      } else if(cb && cb.then) {
        oldVal = this.$value;
        cb.then(function(value) {
          newVal = jsonpath ?
            jsonPath(value, jsonpath) :
            value;
          _self.$value = newVal;
          _self.change(newVal, oldVal);
        });
      } else if(!angular.isFunction(cb)) {
        oldVal = _self.$value;
        newVal = jsonpath ?
          jsonPath(cb, jsonpath) :
          cb;
        _self.$value = newVal;
        this.change(newVal, oldVal);
      } else {
        oldVal = this.$value;
        newVal = cb(this.$value);
        this.$value = newVal;
        this.change(newVal, oldVal);
      }
      return this;
    };