lazyer

Lazyer

Lazy iteration in JavaScript.
Based heavily on the Rust iterator trait.

Overview

Lazyer allows for lazy iteration.
It can be used for working with finite sequences:

const lazy = require('lazyer');
lazy.for(people)
    .filter(person => person.age >= 65)
    .map(person => `${person.firstName} ${person.lastName}`)
    .map(name => name.toUpperCase())
    .forEach(name => console.log(name));
// That was all one iteration!

And infinite sequences:

const lazy = require('lazyer');
const fibonacci = lazy.range(0, Infinity)
    .scan(([a, b]) => [b, a + b], [0, 1])
    .map(([a]) => a)
    .take(10)
    .collect();
console.log(fibonacci);
// → [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Works with anything iterable:

const lazy = require('lazyer');
const string = 'Hello World!';
const set = new Set(string);
const map = lazy.range(0)
    .zip(set)
    .collectMap();
console.log(map);
/* → Map {
    0 => 'H',
    1 => 'e',
    2 => 'l',
    3 => 'o',
    4 => ' ',
    5 => 'W',
    6 => 'r',
    7 => 'd',
    8 => '!' } */

And does a bunch of useful things:

const lazy = require('lazyer');
const longest = lazy.for(listOfListOfNodes)
    .flatten()
    .flatMap(node => node.children)
    .max(node => node.data.length);
console.log(longest);
// Simple!

Functions

Functions that create a lazy iterator.

• for
• of
• range
• repeat
• repeatWith
• iterate

Adaptors

Methods that adapt the iterator.
A consumer needs to be called before any of these will be executed.

• stepBy
• skip
• take
• skipWhile
• takeWhile
• chunk
• enumerate
• concat
• cycle
• map
• filter
• scan
• zip
• flatten
• flatMap
• join
• joinWith
• each

Consumers

Methods that consume the iterator.
These methods start the iteration.

• next
• peek
• at
• count
• last
• forEach
• reduce
• sum
• product
• find
• findIndex
• every
• some
• max
• min
• maxBy
• minBy
• collect
• partition
• unzip
• group
• categorize
• clone
• cloneMany

Docs

See the documented source code.
And for examples, see the test file.