co-reduce-any

Reduce anything in Co-like manner

Provides a consistent interface for reducing arrays, strings, object literals, maps, sets, generators and streams. Synchronously whenever possible.

Installation

yarn add co-reduce-any
npm i -S co-reduce-any

Usage

reduce behaves like Co, except it's supplied with helper next object. Yielding next returns next pair of the iteration or undefined when there are no more elements.

Additionally if no promises were yielded, function returns by value. Always returns a promise when iterating over streams.

const reduce = require("co-reduce-any")

const collection = [ 1, 2, 3, 4 ]

reduce(collection, function* (next) {
    const result = [ ]
    for (let pair; pair = yield next;) {
        const [ key, elem ] = pair
        const value = yield Promise.resolve(elem * key)
        result.push(value)
    }
    return result
}).then(result => console.log(result))

Key points:

value = yield promise // extract value from promise or throw, just like Co
yield next            // waits for next [ key, element ] pair

What's the pair?

Pair is a 2-element array containing in order the key and the value of current element.

• In arrays and strings, key is the elements' index
• In ES6 Maps and object literals, key is the element's key
• In generators, ES6 Sets and node streams, key is the iteration's "i" provided for consistency

It's to preserve consistency with for...of loop over ES6 Map. That way you can write algorithms that work on any kind of collection.