#2775 - Undefined to Null

Medium • View on LeetCode • View on GitHub

Problem Description

Given a deeply nested object or array obj, return the object obj with any undefined values replaced by null.

undefined values are handled differently than null values when objects are converted to a JSON string using JSON.stringify(). This function helps ensure serialized data is free of unexpected errors.

Solution

/**
 * @param {Object|Array} obj
 * @return {Object|Array}
 */
var undefinedToNull = function(obj) {
  if (obj === undefined) {
    return null;
  }

  if (obj === null || typeof obj !== 'object') {
    return obj;
  }

  if (Array.isArray(obj)) {
    return obj.map(item => undefinedToNull(item));
  }

  const result = {};
  Object.keys(obj).forEach(key => {
    result[key] = undefinedToNull(obj[key]);
  });

  return result;
};