JavaScript map and filter object extensions

object+map+filter.js

 /********************
   * Object modifiers
   ********************/

  /**
   * Object.mapObject(value,key)
   * Map Object properties
   * @return object Copy of this object
   */
  if( typeof( Object.mapObject ) == 'undefined') {
    Object.defineProperty(Object.prototype, 'mapObject', {
      value: function(f, ctx) {
          ctx = ctx || this;
          var self = this, result = {};
          Object.keys(self).forEach(function(k) {
              result[k] = f.call(ctx, self[k], k, self);
          });
          return result;
      }
    });
  }

  /**
   * Object.filterObject(value,key)
   * Filter object properties
   * @return object This object modified
   */
  if( typeof( Object.filterObject ) == 'undefined') {
    Object.defineProperty(Object.prototype, 'filterObject', {
      value: function(f, ctx) {
          ctx = ctx || this;
          var self = this, result = {};
          Object.keys(self).filter(v => { return ( !f.call(ctx, self[v], v, self) ) }).forEach(v => { delete self[v]; } ) 
      }
    });
  }

Usage:

var zoo = {
 animals : 100,
 zookeeper : 3,
 kinds : ["tiger", "elephant", "lion"]
}

aquarium=zoo.mapObject((v,k) => { if( k=='kinds') v.push('platypus'); return this[k]=v })
console.log(aquarium)

aquarium.filterObject((v,k) => { return k=='kinds' })
console.log(aquarium)