Deep merge two objects

deep-merge.ts

export type DeepPartial<T> = {
  [P in keyof T]?: DeepPartial<T[P]>;
};


function isObject(item: any): boolean {
  return item && typeof item === 'object' && !Array.isArray(item);
}

export function merge<T>(target: T, source: DeepPartial<T>): T {
  for (const key in source) {
    const targetValue = target[key];
    const sourceValue = source[key];

    if (sourceValue === undefined) {
      continue;
    }

    if (isObject(targetValue) && isObject(sourceValue)) {
      target[key] = merge(targetValue, sourceValue);
    } else {
      target[key] = sourceValue as T[typeof key];
    }
  }
  return target;
}