objectMergeDeep.js

export function objectMergeDeep(target, source) {
  Object.keys(source).forEach(key => {
    const targetValue = target[key];
    const sourceValue = source[key];

    if (typeof sourceValue === 'object' && sourceValue !== null) {
      if (typeof targetValue === 'object' && targetValue !== null) {
        objectMergeDeep(targetValue, sourceValue);
      } else {
        target[key] = (Array.isArray(sourceValue)) ? [] : {};
        objectMergeDeep(target[key], sourceValue);
      }
    } else {
      target[key] = sourceValue;
    }
  });
  return target;
}