@wasmuth/filter/filter.js

Practical, functional utilities that fallback on native implementations as much as possible

import check from 'check-arg-types'

import partial from '@wasmuth/partial'

const toType = check.prototype.toType

/**
 * Functional, curryable wrapper around native Array.filter implementation
 * @param  {Function} fn
 * @param  {Array}    ls
 * @return {Array}
 */
export default function filter (fn, ls) {
  if (arguments.length < 2) return partial(filter, arguments)
  check(arguments, ['function', ['array', 'object']])
  return toType(ls) === 'array'
    ? Array.prototype.filter.call(ls, fn)
    : objFilter(fn, ls)
}

function objFilter (fn, obj) {
  const keys = Object.keys(obj)
  const len = keys.length
  const result = {}
  for (let x = 0; x < len; x++) {
    if (fn(obj[keys[x]], keys[x])) {
      result[keys[x]] = obj[keys[x]]
    }
  }
  return result
}