Custom Fuzzy Filter AngularJS Pipe against ambiguous iterable types (i.e. List of Objects of Arrays of Objects of ... [etc.])

fuzzy.filter.js

(function () {
  'use strict';

  angular.module('app')
  .filter('fuzzyFilter', FuzzyFilter);

  /**
   * Flattens an array<any> into an array of elements
   * where the elements contain only literals (i.e. Strings, Numbers, Booleans)
   * @param  {Array<any>} arr                      an iterable to flatten
   * @return {Array<Array<String|Number|Boolean>>} an array of array elements containing literals
   */
  function flatten(arr) {
    return arr.map(function (el) {
      if (el instanceof Array) {
        return flatten(el);
      } else if (el instanceof Object) {
        return flatten(Object.keys(el).map(function (key) { return el[key]; }));
      } else {
        return el;
      }
    });
  }

  /**
   * Loops through any nested elements and checks against the callback for matching
   * @param  {Array<any>} arr  an iterable to find a matching element
   * @param  {Function}   cb   a callback that must return either truthful or falsy values
   * @return {Boolean}         the result of whether a match was found or not
   */
  function isMatching(arr, cb) {
    return arr.reduce(function (prev, next) {
      if (next instanceof Array) { return prev || isMatching(next, cb); }
      else { return prev || Boolean(cb(next)); }
    }, false);
  }

  /**
   * Pipes the input through a flatten and exposes each
   * input literal within to a provided callback function
   * @return {Array<any>} the filtered list
   */
  function FuzzyFilter() {
    /**
     * Filter function to use in Angular JS pipe operations
     * @param  {Array<any>} inputArray an iterable list to filter
     * @param  {Function}   cb         a callback that must return either truthful or falsy values
     * @return {Array<any>}            the filtered list
     */
    return function (inputArray, cb) {
      return flatten(angular.copy(inputArray)).map(function (el, idx) {
        if (isMatching(el, cb)) return inputArray[idx];
        else return undefined;
      }).filter(function (el) { return el !== undefined; });
    };
  }

})();