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Lazy.js

MITJavaScript

A functional JavaScript utility library with lazy evaluation for optimal performance and memory efficiency.

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6.0k stars260 forks0 contributors

What is Lazy.js?

Lazy.js is a functional utility library for JavaScript that provides lazy evaluation of sequences, similar to Underscore and Lodash. It solves performance and memory issues by deferring computations until needed, avoiding intermediate arrays and unnecessary iterations. This makes it ideal for processing large datasets, infinite sequences, and event streams efficiently.

Target Audience

JavaScript developers working with data transformations, large arrays, or streams who need better performance and memory efficiency than standard utility libraries offer. It's also useful for developers handling DOM events or asynchronous sequences functionally.

Value Proposition

Developers choose Lazy.js because it offers the familiar API of Underscore/Lodash with the performance of hand-written procedural code, thanks to its lazy engine. It uniquely supports indefinite sequences, asynchronous iteration, and event/stream processing without sacrificing expressiveness.

Overview

Like Underscore, but lazier

Use Cases

Best For

  • Processing large arrays with chained transformations (e.g., filtering and mapping) without memory overhead
  • Generating and manipulating infinite sequences like random numbers or mathematical series
  • Handling DOM events as functional sequences for reactive UI logic
  • Efficiently splitting or matching patterns in large strings without full array creation
  • Lazily reading and processing Node.js file or HTTP streams line-by-line
  • Implementing search-as-you-type functionality with early termination (e.g., take first N matches)

Not Ideal For

  • Projects requiring stable, production-ready libraries with no breaking changes
  • Teams deeply integrated with Lodash's ecosystem or third-party plugins
  • Applications where immediate array results are frequently needed without lazy evaluation

Pros & Cons

Pros

Efficient Large Data Processing

Lazy evaluation defers computation until needed, eliminating intermediate arrays as shown in the search example with a people array, reducing memory overhead for chained transformations.

Indefinite Sequence Support

Can generate infinite sequences like random numbers or Fibonacci, enabling transformations without pre-computation, as demonstrated in the README with Math.random and Fibonacci examples.

Asynchronous Workflow Control

Allows timed intervals between elements with the async method, useful for controlled iteration, like outputting characters with a 1-second delay.

Event Stream Handling

Treats DOM events as sequences for functional operations like map and filter, shown in the mousemove example with coordinate mapping and filtering.

Memory-Efficient String Operations

Splits strings or matches patterns lazily without creating full arrays, ideal for large text processing, as illustrated with taking the first five lines of a string.

Cons

Experimental Status

The library is marked as experimental with API changes likely, especially for stream processing as noted in the README, making it risky for long-term projects.

Limited Browser Support Setup

Requires a separate file (lazy.browser.js) for DOM event handling, adding complexity and extra steps for frontend integration compared to all-in-one solutions.

Ecosystem Maturity

Compared to Lodash, it has fewer features, plugins, and community contributions, which can limit customization and support for edge cases.

Open Source Alternative To

Lazy.js is an open-source alternative to the following products:

Lodash
Lodash

Lodash is a popular JavaScript utility library that provides consistent, modular functions for common programming tasks like array manipulation, object iteration, and function composition.

U
Underscore

Underscore is a JavaScript utility library that provides functional programming helpers for working with arrays, objects, and functions.

Frequently Asked Questions

Quick Stats

Stars5,972
Forks260
Contributors0
Open Issues53
Last commit6 years ago
CreatedSince 2013

Tags

#stream-processing#functional-programming#utility-library#javascript#data-processing#event-handling#string-manipulation#lazy-evaluation#performance

Built With

J
JavaScript

Links & Resources

Website

Included in

JavaScript34.9kFunctional Programming6.0kEmber202
Auto-fetched 19 hours ago

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