Creating read-only JS object

gistfile1.js

// lo-dash lib is the dependency

function readOnly(target){
  var _readOnly = function (target, acc) {
          
    // acc is passed into the function to be used for observer
    var _defineProperty = function (propName, target, acc) {
      var i, len;
      
      // operation to be performed when add occurred
      var addOp = function (cArg) {
        // have to define the added item
        _defineProperty(cArg.name, cArg.object, acc[propName]);
      };
        
      // operation to be performed when add delete
      var delOp = function (cArg) {
        if (_.isPlainObject(cArg.object)) {
          delete acc[propName][cArg.name];
        }
        if (_.isArray(cArg.object)) {
          // this fixes the array
          acc[propName].unshift(acc[propName].shift());

          // when splice occures, there's no 
          // clear indication what has been removed
          // so, we need to find the diff, and clear acc
          var args = _.difference(acc[propName], cArg.object);
          args.unshift(acc[propName]);
          _.pull.apply(null, args);
        }
      };
        
      // function that is called when any change in the property happens
      var observeFn = function (changes) {
        for (i = 0, len = changes.length; i < len; i += 1) {
          switch(changes[i].type) {
            case 'new':
              addOp(changes[i]);
              break;
            case 'deleted':
              delOp(changes[i]);
              break;
            default:
              continue;
          }
        }
      };
      
      if (_.isArray(target[propName])) {
        Object.defineProperty(acc, propName, {
          configurable: true,
          enumerable: true,
          value: []
        });
        Object.observe(target[propName], observeFn);
        _readOnly(target[propName], acc[propName]);
      }
      else if (_.isPlainObject(target[propName])) {
        Object.defineProperty(acc, propName, {
          configurable: true,
          enumerable: true,
          value: {}
        });
        Object.observe(target[propName], observeFn);
        _readOnly(target[propName], acc[propName]);
      }
      // value is the primitive one
      else {
        Object.defineProperty(acc, propName, {
          configurable: true,
          enumerable: true,
          get: function () {
            return target[propName];
          }
        });
      }
    };
    
    // target is an array
    _.forEach(target, function (val, key) {
      _defineProperty(key, target, acc);
    });
    
    return acc;
  };
  if (Array.isArray(target)) {
    return _readOnly(target, []);
  }
  else {
    return _readOnly(target, {});
  }
}