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Array methods are eager. Iterator helpers are lazy. Here's why that matters.
TL;DR: Iterator helpers enable lazy data processing in JavaScript, avoiding intermediate arrays when chaining operations. They let you build a pipeline that only processes elements as needed, which is especially beneficial for large or infinite data sources.
Arrays are eager: each chain creates and materializes full intermediate arrays. Iterator helpers wrap any iterable into a lazy pipeline; two phases exist: building the pipeline and running it. No elements are processed until a terminal method requests results. This allows early termination (e.g., first 50 matches) without iterating the entire set, and supports infinite or large datasets via on-demand generation.
Question for the room: Have you migrated any performance-critical code to use iterator helpers for lazy evaluation, and what impact did it have on memory or latency?
— via dev.to
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