imlazy
A functional programming library for creating lazy, immutable iterables using ES2015 iteration protocols.
What is imlazy?
imlazy is a JavaScript library for functional programming with lazy, immutable iterables. It allows developers to create and manipulate infinite or circular sequences using ES2015 iteration protocols, providing a performant and memory-efficient way to handle data streams. The library emphasizes purity and composability with auto-curried functions and seamless integration with native JavaScript iterables.
JavaScript developers working with functional programming paradigms, data transformation pipelines, or large/infinite datasets who need lazy evaluation and immutability. It's particularly useful for those familiar with libraries like Ramda or Immutable.js.
Developers choose imlazy for its strict adherence to functional principles, compatibility with ES2015 iteration protocols, and ability to handle infinite sequences without performance overhead. Its auto-curried API and Static Land algebraic type implementations offer a robust foundation for composable data processing.
Overview
😴 Functional programming with lazy immutable iterables
Use Cases
Best For
- Creating and manipulating infinite sequences (e.g., number ranges, Fibonacci generators)
- Building functional data transformation pipelines with lazy evaluation
- Working with large datasets where memory efficiency is critical
- Integrating with ES2015 iterables (Arrays, Sets, Maps, Generators) in a functional style
- Implementing algebraic functional programming patterns (Functors, Monads, Foldables)
- Debugging nested or infinite iterables with custom string representations
Not Ideal For
- Performance-critical applications where native array methods are sufficient
- Teams without prior experience in functional programming or curried APIs
- Projects requiring mutable data structures for frequent in-place updates
- Environments lacking ES2015 iteration protocol support (e.g., older browsers or Node.js <6)
Pros & Cons
Pros
Enables creation of unbounded data streams like `range(1, Infinity)` that compute values on-demand, preventing memory bloat for large or infinite datasets.
Works with native iterables (Array, Set, Map) and third-party libraries like Immutable.js, as shown in examples summing values from different sources.
Auto-curried, iterable-last functions support partial application, allowing reusable pipelines like `takeThree = take(3)` for easy chaining.
All generated iterables are frozen with `Object.freeze`, ensuring they cannot be accidentally modified, which aligns with functional purity.
Provides a custom LISP-like string representation for inspecting nested or infinite iterables, listing first 10 elements with ellipsis for clarity.
Cons
Benchmarks in the README show operations like filter and map are significantly slower than native JavaScript methods, with up to 10x lower ops/sec for array transformations.
Requires familiarity with functional programming concepts like currying, algebraic types, and lazy evaluation, which may alienate developers from imperative backgrounds.
The library focuses on synchronous iterables and does not explicitly support asynchronous iteration protocols, restricting use in modern async/await workflows.
Frequently Asked Questions
Related Projects
immutableImmutable persistent data collections for Javascript which increase efficiency and simplicity.
ImmerCreate the next immutable state by mutating the current one
Lazy.jsLike Underscore, but lazier
moriClojureScript's persistent data structures and supporting API from the comfort of vanilla JavaScript
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