LazyIterable

A lightweight, powerful library that provides wrapper classes and utility functions for lazily-evaluating data structures, including support for async sources, and built completely with native JavaScript features.

Motivation

This package was motivated by my desire to learn how generators work in JavaScript, and then spiralled into learning how to setup and publich a fully featured NPM package. It was partly inspired by the pythonic package.

It is written in TypeScript, tested with Jest, linted with ESLint, formatted with Prettier, bundled with Rollup, and documented with TSDoc.

Installation

Using npm:

npm install @jderrington/lazy-iterable

Using yarn:

yarn add @jderrington/lazy-iterable

Importing

const {LazyIterable} = require("@jderrington/lazy-iterable");
// Or
import {LazyIterable} from "@jderrington/lazy-iterable";

Using script tags:

/* Take the index.js file from the dist/ folder */
<script src="index.js"></script>
<script>
/* Imports are under the 'LazyIterableLib' name */
const {LazyIterable} = LazyIterableLib;
</script>

Usage

See the documentation for full the full API specification and examples. There are also examples of usage with Node streams and pagination.

Provides Python and Haskell style functions such as enumerate, range, zip and repeat, as well as lazy methods such as take, and drop (and many more).

// Track the index in a for loop instead of requiring `forEach`
for (const [index, value] of enumerate([1, 2, 3, 4, 5])) {
  // Loop body
}

// Python style range iteration
for(const i of range(0, 5)) {
  // Loop body
}

// Haskell style lazy evaluation
repeat(5).take(5).toArray() // Returns [5, 5, 5, 5, 5]

// Use familiar array methods on infinite data sources
infinite()
  .map((value, index) => `${index}: ${value}`)
  .take(3)
  .join(", "); // Returns "0: 1, 1: 2, 2: 3"