Checkout our solution:

One possible implementation could be:

function filter(collection, callback) {
  // DO NOT REMOVE
  'use strict';

  // write your code below

  const isCollectionInvalid =
    !collection ||
    collection === null ||
    typeof collection !== 'object' ||
    Array.isArray(collection);
  const isCallbackInvalid = !callback || typeof callback !== 'function';

  // early escape if input params are incorrect
  if (isCollectionInvalid || isCallbackInvalid) {
    throw new TypeError('Invalid params');
  }

  const output = {};

  function processing(result, input) {
    // looping over the properties inside the collection
    for (const property in input) {
      // checking only direct properties of the collection
      if (Object.prototype.hasOwnProperty.call(input, property)) {
        const current = input[property];

        // condition to check objects
        if (typeof current === 'object' &amp;&amp; current !== null) {
          const nestedObject = {};

          processing(nestedObject, current);

          // only to include nested object with keys
          if (nestedObject &amp;&amp; Object.keys(nestedObject).length) {
            result[property] = nestedObject;
          }
        } else if (callback(current)) {
          // setting the value if callback returns truthy value
          result[property] = current;
        }
      }
    }
  }

  // starts processing with empty object
  processing(output, collection);

  // returning the filtered object
  return output;
}

Our submission:

https://devtools.tech/questions/implement-deep-filter-or-aws-frontend-interview-question-or-javascript-or-problem-solving-or-amazon/submissions/OXyVVdQeEgv0qILFYzUe

Do you see value in our efforts?

How to implement Deep Filter Functionality? | AWS Frontend Interview Question | JavaScript | Problem Solving | Amazon

@Devtools Tech