function receiveHandlerId(handlerId) {
	    if (handlerId === currentHandlerId) {
	      return;
	    }

	    currentHandlerId = handlerId;
	    reconnectDropTarget();
	  }
This method is like `_.assignIn` except that it accepts `customizer`
which is invoked to produce the assigned values. If `customizer` returns
`undefined`, assignment is handled by the method instead. The `customizer`
is invoked with five arguments: (objValue, srcValue, key, object, source).

**Note:** This method mutates `object`.

@static
@memberOf _
@since 4.0.0
@alias extendWith
@category Object
@param {Object} object The destination object.
@param {...Object} sources The source objects.
@param {Function} [customizer] The function to customize assigned values.
@returns {Object} Returns `object`.
@see _.assignWith
@example

function customizer(objValue, srcValue) {
  return _.isUndefined(objValue) ? srcValue : objValue;
}

var defaults = _.partialRight(_.assignInWith, customizer);

defaults({ 'a': 1 }, { 'b': 2 }, { 'a': 3 });
// => { 'a': 1, 'b': 2 }