JavaScript: convert format of object keys between camel-case and snake-case

camelSnake.js

/**
 * @param {Object|String} data string or keys of object are named in form of snake
 * @param {number} depth to which level of keys should it process
 * @return {Object|String} string or keys of object are named in form of camel case
 */
exports.snakeToCamel = function(data, depth) {
  if (Util.isObject(data)) {
    if (typeof depth === 'undefined') {
      depth = 1;
    }
    return _processKeys(data, _camelize, depth);
  } else {
    return _camelize(data);
  }
};

/**
 * @param {Object|String} data string or keys of object are named in form of camel case
 * @param {number} depth to which level of keys should it process
 * @return {Object|String} string or keys of object are named in form of snake
 */
exports.camelToSnake = function(data, depth) {
  if (Util.isObject(data)) {
    if (typeof depth === 'undefined') {
      depth = 1;
    }
    return _processKeys(data, _snakelize, depth);
  } else {
    return _snakelize(data);
  }
};

// snakelize a string formed in underscore
function _snakelize(key) {
  let separator = '_';
  let split = /(?=[A-Z])/;

  return key.split(split).join(separator).toLowerCase();
}

// camelize a string formed in underscore
function _camelize(key) {
  if (Util.isNumber(key)) {
    return key;
  }
  key = key.replace(/[\-_\s]+(.)?/g, function(match, ch) {
    return ch ? ch.toUpperCase() : '';
  });
  // Ensure 1st char is always lowercase
  return key.substr(0, 1).toLowerCase() + key.substr(1);
}

// camelize/snakelize keys of an object
// @param {number} depth to which level of keys should it process
function _processKeys(obj, processer, depth) {
  if (depth === 0 || !Util.isObject(obj)) {
    return obj;
  }

  let result = {};
  let keys = Object.keys(obj);

  for (let i = 0; i < keys.length; i++) {
    result[processer(keys[i])] = _processKeys(obj[keys[i]], processer, depth - 1);
  }

  return result;
}