#2823 - Deep Object Filter

Problem Description

Given an object or an array obj and a function fn, return a filtered object or array filteredObject.

Function deepFilter should perform a deep filter operation on the obj. The deep filter operation should remove properties for which the output of the filter function fn is false, as well as any empty objects or arrays that remain after the keys have been removed.

If the deep filter operation results in an empty object or array, with no remaining properties, deepFilter should return undefined to indicate that there is no valid data left in the filteredObject.

Solution

/**
 * @param {Object|Array} obj
 * @param {Function} fn
 * @return {Object|Array|undefined}
 */
var deepFilter = function(obj, fn) {
  if (Array.isArray(obj)) {
    const filteredArray = obj
      .map(item => deepFilter(item, fn))
      .filter(item => item !== undefined);

    return filteredArray.length > 0 ? filteredArray : undefined;
  }

  if (typeof obj === 'object' && obj !== null) {
    const filteredObject = {};
    let hasValidProperties = false;

    Object.keys(obj).forEach(key => {
      const filteredValue = deepFilter(obj[key], fn);
      if (filteredValue !== undefined) {
        filteredObject[key] = filteredValue;
        hasValidProperties = true;
      }
    });

    return hasValidProperties ? filteredObject : undefined;
  }

  return fn(obj) ? obj : undefined;
};