cherryPick - recurse any value, including objects and arrays, returning an array of values that match the predicate

cherryPick.js

// @flow

type Predicate<T> = T => boolean

export default function cherryPick<T>(memo: Array<T>, predicate: Predicate<T>, subject: T): Array<T> {
  if (predicate(subject)) {
    return [ ...memo, subject ]
  }
  if (Array.isArray(subject)) {
    return subject.reduce((memo, subject) => cherryPick(memo, predicate, subject), memo)
  }
  if (subject instanceof Object) {
    return Object.keys(subject).reduce((memo, key) => {
      // $FlowFixMe: missing indexer property
      return cherryPick(memo, predicate, subject[key])
    }, memo)
  }
  return memo
}

example.js

import cherryPick from './cherryPick'

const data = {
  name: 'Bob',
  age: 40,
  children: [
    {
      name: 'Harry',
      age: 10
    },
    { 
      name: 'Alice',
      age: 13
    }
  ],
  spouse: {
    name: 'Susan',
    age: 38
  }
};

const childPredicate = subject => typeof subject === 'object' && subject.age <= 16;
const children = cherryPick([], childPredicate, data);