@primacode/iterate

Lazy operations on Iterable<T>

This package is a set of utils functions for working with JavaScript iterators and Iterable<T>.

• Lazy-evaluated - reduce memory usage on big data sets.
• Built on top of native Iterable<T> - stick to well-established standards.
• Fully tree-shakable - add minimal code overhead.
• TypeScript support - leverage static type checking and code hints.
• Functional programming approach - use the best modern practices.
• Mimics array API - easy to understand and get started.

Inspired by wu.js, rxjs and LINQ.

Quickstart

Install the library:

npm install --save @primacode/iterate

Import and you're good to go:

import { iterate, filter } from '@primacode/iterate';

iterate([1, 2, 3])(filter(x => x < 3));

Lazy evaluation

Lazy evaluation means that operations are executed just-in-time, instead of executing them eagerly.

For example - eagerly-evaluated JS code is:

const result = [1, 2, 3]
  .filter(x => x < 3)
  .map(x => 'a' + x);

The main drawback is that it creates an array for each step in the process:

const result = [1, 2, 3]
  .filter(x => x < 3)                 // -> [1, 2]
  .map(x => 'a' + x);                 // -> ['a1', 'a2']

In this case, lazy evaluation means processing data on the fly and creating only single array at the end. It can be particularly useful when working with large data sets.

@primacode/iterate provides convenient API for doing this:

const result = iterate([1, 2, 3])(
  filter(x => x < 3),                 // -> Iterable<number>
  map(x => 'a' + x),                  // -> Iterable<string>
  toArray                             // -> ['a1', 'a2']
);

It's also possible to efficiently iterate the data, without creating an array:

const iterable = iterate([1, 2, 3])(filter(x => x < 3));

for (const item of iterable) {
  // item = 1
  // item = 2
}

References

• typescript-starter - Quickly create and configure a new library or Node.js project.
• wu.js - JavaScript library providing higher order functions for ECMAScript 6 iterators.
• rxjs - Reactive extensions for JavaScript.