propertyIsEnumerable

Definition: The propertyIsEnumerable method of each object is used to find out whether a given property will be included or excluded when a for (x in y) loop is processed. Properties that are enumerable will be included in the loop while those that are not enumerable will be ignored. This is not a reserved word so you can declare your own variable or function called propertyIsEnumerable but if you do then you will not be able to perform this test.