next.js/packages/next/src/next-devtools/shared/deepmerge.ts

export function deepMerge(target: any, source: any): any {
  if (!source || typeof source !== 'object' || Array.isArray(source)) {
    return source
  }

  if (!target || typeof target !== 'object' || Array.isArray(target)) {
    return source
  }

  const result = { ...target }

  for (const key in source) {
    const sourceValue = source[key]
    const targetValue = target[key]

    if (sourceValue !== undefined) {
      if (
        sourceValue &&
        typeof sourceValue === 'object' &&
        !Array.isArray(sourceValue) &&
        targetValue &&
        typeof targetValue === 'object' &&
        !Array.isArray(targetValue)
      ) {
        result[key] = deepMerge(targetValue, sourceValue)
      } else {
        result[key] = sourceValue
      }
    }
  }

  return result
}