deep-clone.ts

// TS does not allow for circular types, but there is a trick with interfaces:
// https://github.com/Microsoft/TypeScript/issues/3496#issuecomment-128553540
// eslint-disable-next-line no-use-before-define
type DeepCloneSupportedType = boolean | number | bigint | string | undefined | null | Date | IDeepCloneSupportedTypeObject | IDeepCloneSupportedTypeArray;

interface IDeepCloneSupportedTypeObject {
  [x: string]: DeepCloneSupportedType;
}

// the part of the trick above
// eslint-disable-next-line @typescript-eslint/no-empty-interface
interface IDeepCloneSupportedTypeArray extends Array<DeepCloneSupportedType> { }

/**
 * WARNING!
 *
 * There is a problem with __proto__ support in TypeScript. Since our tests are written in TypeScript,
 * we don't test this helper. Please be careful when changing this function!
 *
 * @deprecated since v8.9.0 - use structuredClone instead
 * @see https://developer.mozilla.org/en-US/docs/Web/API/structuredClone
 */
function deepClone<T extends DeepCloneSupportedType>(obj: T): T;
function deepClone(obj: DeepCloneSupportedType): DeepCloneSupportedType {
  if (obj == null || typeof obj !== 'object') {
    return obj;
  }

  if (obj instanceof Date) {
    const copy = new Date();
    copy.setTime(obj.getTime());
    return copy;
  }

  if (obj instanceof Array) {
    const copy: IDeepCloneSupportedTypeArray = [];
    for (let i = 0, len = obj.length; i < len; i++) {
      copy[i] = deepClone(obj[i]);
    }
    return copy;
  }

  const copy: typeof obj = {};

  Object.keys(obj).forEach(key => {
    const value = deepClone(obj[key]);

    // The __proto__ property has a special meaning in JavaScript. So, to prevent prototype poisoning,
    // we restrict direct assignment to this property.
    if (key === '__proto__') {
      Object.defineProperty(copy, key, {
        configurable: true,
        enumerable: true,
        value,
        writable: true,
      });
    } else {
      copy[key] = value;
    }
  });

  return copy;
}

export default deepClone;