Iterators & Generators in Node.js

Deep dive into iterators and generators in JavaScript and Node.js: iteration protocols, custom iterators, generator functions, lazy evaluation, infinite sequences, async generators, and real-world backend use cases.

Why Iterators & Generators Matter

Iterators and generators give developers low-level control over how data is produced and consumed. They enable lazy evaluation, memory-efficient processing, and fine-grained execution control, which are essential in advanced backend systems.

1. Execution Control Model

Pull-based data flow.

The Iteration Protocol

JavaScript iteration is based on a well-defined protocol using Symbol.iterator and next().

1. Iterator Structure

next() contract.

2. Built-in Iterables

Objects that implement Symbol.iterator.

Creating Custom Iterators

Custom iterators allow precise control over iteration behavior.

1. Custom Iterator Object

Implementing Symbol.iterator.

Generator Functions

Generators automatically implement the iterator protocol and provide pause-resume semantics.

1. Basic Generator

yield keyword.

2. Generator State Control

Manual next calls.

Lazy Evaluation

Generators allow values to be produced only when needed.

1. Infinite Generator

Unbounded sequences.

Backend Use Cases

Generators shine when dealing with large datasets and controlled execution.

1. Batch Processing

Process data in chunks.

Async Generators

Async generators combine generators with promises.

1. Async Generator Function

await + yield.

Pitfalls & Best Practices

Iterators and generators are powerful but easy to misuse.

1. Recommended Guidelines

Production rules.