Module iterator 

Iterator helpers (27.1.4) — map, filter, take, drop, flatMap and the terminal reduce/toArray/forEach/some/every/find, plus the Iterator constructor and Iterator.from.

None of it existed: [1,2,3].values().map(f) was “map is not a function”.

The helpers are LAZY, which is the whole point of them — take(3) on an endless generator has to stop after three pulls, not materialise anything. Each is an @@native = "IteratorHelper" object holding the iterator it draws from, so a chain is a chain of pulls; only the terminal operations drain. That also makes them work over any iterator, including a user object with a next method.

Constants

LAZY

The lazy helpers, which return another iterator.

METHODS

Everything Iterator.prototype carries, so any iterator answers for it.

STATIC_METHODS

Iterator’s own statics.

TERMINAL

The terminal operations, which drain the iterator and return a value.

Functions

call

Dispatch a helper called on the iterator recv.

done_step

The { value: undefined, done: true } an exhausted iterator reports.

helper_next

One step of a lazy helper: pull from the source until this stage produces a value or the source runs out.

helper_return

Mark a helper exhausted and close whatever it was drawing from — a return on any stage of a chain has to reach the generator at the bottom of it.

is_helper

True if name is one of the helper methods (lazy or terminal).

static_call

Iterator.from(x).