code: function _arrayOp(arrayFn, opArgs) {
  		var res
  		var key = opArgs[1]
  		var rest = slice(opArgs, 2)
  		this.update(key, [], function(arrVal) {
  			res = Array.prototype[arrayFn].apply(arrVal, rest)
  		})
  		return res
  	}
docs: internal /////////