date-fns/constructFrom.js

import { constructFromSymbol } from "./constants.js";

/**
 * @name constructFrom
 * @category Generic Helpers
 * @summary Constructs a date using the reference date and the value
 *
 * @description
 * The function constructs a new date using the constructor from the reference
 * date and the given value. It helps to build generic functions that accept
 * date extensions.
 *
 * It defaults to `Date` if the passed reference date is a number or a string.
 *
 * Starting from v3.7.0, it allows to construct a date using `[Symbol.for("constructDateFrom")]`
 * enabling to transfer extra properties from the reference date to the new date.
 * It's useful for extensions like [`TZDate`](https://github.com/date-fns/tz)
 * that accept a time zone as a constructor argument.
 *
 * @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
 *
 * @param date - The reference date to take constructor from
 * @param value - The value to create the date
 *
 * @returns Date initialized using the given date and value
 *
 * @example
 * import { constructFrom } from "./constructFrom/date-fns";
 *
 * // A function that clones a date preserving the original type
 * function cloneDate<DateType extends Date>(date: DateType): DateType {
 *   return constructFrom(
 *     date, // Use constructor from the given date
 *     date.getTime() // Use the date value to create a new date
 *   );
 * }
 */
export function constructFrom(date, value) {
  if (typeof date === "function") return date(value);

  if (date && typeof date === "object" && constructFromSymbol in date)
    return date[constructFromSymbol](value);

  if (date instanceof Date) return new date.constructor(value);

  return new Date(value);
}

// Fallback for modularized imports:
export default constructFrom;