plura/src/filter.js

Super simple functional programming library

const curry = require('./curry')
const { walkArray, walkObject } = require('./utils/walk')
const { isArray, isString } = require('./isType')

/**
 * Simple array filter
 */
const arrayFilter = walkArray(
  (fn, element, result, index) =>
    fn(element, index) ?
      [result.concat(element), false] :
      [result, false]
)

/**
 * Simple object filter
 */
const objectFilter = walkObject(
  (fn, value, key, result, index) =>
    fn(value, index) ?
      [Object.assign({}, result, { [key]: value }), false] :
      [result, false]
)

/**
 * Simple filter
 * @param {Function} fn - function to change values
 * @param {Array||Object||string} collection - somthing to filter over
 * @return {Array||Object||string} _ - collection filtered with fn
 * @example 
 * 
 * const largerThanOne = a => a > 1
 * const array = [1, 2, 3, 4, 0]
 * const result = filter(largerThanOne, array)
 */
const filter = curry(
  (fn, collection) =>
    isArray(collection) || isString(collection)
      ? arrayFilter(fn, collection, [])
      : objectFilter(fn, collection, {})
)

module.exports = filter