voluptasmollitia/packages/util/src/deepCopy.ts

Monorepo for the Firebase JavaScript SDK

/**
 * @license
 * Copyright 2017 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Do a deep-copy of basic JavaScript Objects or Arrays.
 */
export function deepCopy<T>(value: T): T {
  return deepExtend(undefined, value) as T;
}

/**
 * Copy properties from source to target (recursively allows extension
 * of Objects and Arrays).  Scalar values in the target are over-written.
 * If target is undefined, an object of the appropriate type will be created
 * (and returned).
 *
 * We recursively copy all child properties of plain Objects in the source- so
 * that namespace- like dictionaries are merged.
 *
 * Note that the target can be a function, in which case the properties in
 * the source Object are copied onto it as static properties of the Function.
 *
 * Note: we don't merge __proto__ to prevent prototype pollution
 */
export function deepExtend(target: unknown, source: unknown): unknown {
  if (!(source instanceof Object)) {
    return source;
  }

  switch (source.constructor) {
    case Date:
      // Treat Dates like scalars; if the target date object had any child
      // properties - they will be lost!
      const dateValue = source as Date;
      return new Date(dateValue.getTime());

    case Object:
      if (target === undefined) {
        target = {};
      }
      break;
    case Array:
      // Always copy the array source and overwrite the target.
      target = [];
      break;

    default:
      // Not a plain Object - treat it as a scalar.
      return source;
  }

  for (const prop in source) {
    // use isValidKey to guard against prototype pollution. See https://snyk.io/vuln/SNYK-JS-LODASH-450202
    if (!source.hasOwnProperty(prop) || !isValidKey(prop)) {
      continue;
    }
    (target as Record<string, unknown>)[prop] = deepExtend(
      (target as Record<string, unknown>)[prop],
      (source as Record<string, unknown>)[prop]
    );
  }

  return target;
}

function isValidKey(key: string): boolean {
  return key !== '__proto__';
}