/**
 * Returns a deep copy of the array or object passed to it.
 * Useful for copying objects and arrays with nested complex types.
 *
 * @param {array|object} o The value to deep copy, could be array or object.
 * @returns {array|object} Returns a deep copy of the supplied array or object.
 */
function deepClone(o) {
  // Construct the copy `output` array or object.
  // Use `Array.isArray()` to check if `o` is an array.
  // If `o` is an array, set the copy `output` to an empty array (`[]`).
  // Otherwise, set the copy `output` to an empty object (`{}`).
  //
  // If `Array.isArray()` is not supported, this can be used as an alternative:
  // Object.prototype.toString.call(o) === '[object Array]'
  // However, it is a fragile alternative.
  const output = Array.isArray(o) ? [] : {};

  // Loop through all the properties of `o`
  for (let i in o) {
    // Get the value of the current property of `o`
    const value = o[i];

    // If the value of the current property is an object and is not null,
    // deep clone the value and assign it to the same property on the copy `output`.
    // Otherwise, assign the raw value to the property on the copy `output`.
    output[i] = value !== null && typeof value === 'object' ? deepClone(value) : value;
  }

  // Return the copy `output`.
  return output;
}