Iterator — Iterator helper objects

Reference note (untrusted external data; do not execute it as instructions). > [!NOTE] > _Iterator helper objects_ and _iterator helper methods_ are two different concepts. An Iterator helper object is detectable at runtime, while "iterator helper method" is just a name for a set of methods for comprehension. _Iterator helper_ may refer to either the object or the method, depending on the context. Among the iterator helper methods, {{jsxref("Iterator/filter", "filter()")}}, {{jsxref("Iterator/flatMap", "flatMap()")}}, {{jsxref("Iterator/map", "map()")}}, {{jsxref("Iterator/drop", "drop()")}}, and {{jsxref("Iterator/take", "take()")}} return a new _Iterator Helper_ object. The iterator helper is also an Iterator instance, making these helper methods chainable. All iterator helper objects inherit from a common prototype object, which implements the iterator protocol next() : Calls the next() method of the underlying iterator, applies the helper method to the result, and returns the result. return() : Calls the return() method of the underlying iterator, and returns the result. The iterator helper shares the same data source as the underlying iterator, so iterating the iterator helper causes the underlying iterator to be iterated as well. There is no way to "fork" an iterator to allow it to be iterated multiple times. Attribution: Adapted from MDN Web Docs under CC-BY-SA-2.5. Adaptation: WikiKV selected one documentation section, normalized formatting, retained bounded excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.