A JavaScript function to remove null, undefined, empty strings, empty arrays from an object, recursively

removeFalsyKeys.js

/**
 * MIT License
 *
 * Copyright (c) 2024 Paulo Queiroz
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy 
 * of this software and associated documentation files (the "Software"), to 
 * deal in the Software without restriction, including without limitation the 
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or 
 * sell copies of the Software, and to permit persons to whom the Software is 
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next 
 * paragraph) shall be included in all copies or substantial portions of the 
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/**
 * Recursively remove any properties/array elements that are null, undefined, or 
 * empty strings. Additionally, if an array is empty, remove it.
 */
function removeFalsyKeys(obj) {
  const isArray = obj instanceof Array;
  const newArray = [];

  for (const key in obj) {
    // If the value is null, undefined, or an empty string, remove it.
    if (obj[key] === null || obj[key] === undefined || obj[key] === "") {
      // On arrays we don't delete the key, we just skip it. For a value to make 
      // it to an array, it must pass all the checks and be pushed onto 
      // `newArray`.
      if (!isArray) {
        delete obj[key];
      }
    }
    // On elements that are objects, we recursively call `removeNulls` to remove 
    // any null, undefined, or empty string values.
    else if (typeof obj[key] === "object") {
      const newObj = removeFalsyKeys(obj[key]);
      // If obj[key] is an array and it's empty, remove it.
      if (newObj instanceof Array && newObj.length === 0) {
        if (!isArray) {
          delete obj[key];
        }
      }
      // Otherwise we push the new object onto the array 
      else if (isArray) {
        newArray.push(newObj);
      }
      // Or replace the old object with the new object.
      else {
        obj[key] = newObj;
      }
    }
    // If all checks passed and we are dealing with an array, push the value onto 
    // `newArray`.
    else if (isArray) {
      newArray.push(obj[key]);
    }
  }

  return isArray ? newArray : obj;
}

Example:

const exampleObj = {
  name: "John",
  age: null,
  address: {
    street: "1234 Elm St",
    city: null,
    state: "",
  },
  gears: {
    "a": "",
    "b": null,
  },
  phoneNumbers: [
    "123-456-7890",
    null,
    "",
    ["aaaa", null, "", ["", null, null, [[[]]]], ["", ["aaa"]]]
  ],
  something: ["", null, ""],
};

console.log(removeFalsyKeys(exampleObj));

Output:

{
  name: 'John',
  address: { street: '1234 Elm St' },
  gears: {},
  phoneNumbers: [
    '123-456-7890',
    [ 'aaaa', [ [ 'aaa' ] ] ]
  ]
}