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index.ts
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index.ts
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import { constructFrom } from "../constructFrom/index.js";
import { toDate } from "../toDate/index.js";
import type { ContextOptions, DateArg } from "../types.js";
/**
* The {@link addDays} function options.
*/
export interface AddDaysOptions<DateType extends Date = Date>
extends ContextOptions<DateType> {}
/**
* @name addDays
* @category Day Helpers
* @summary Add the specified number of days to the given date.
*
* @description
* Add the specified number of days to the given date.
*
* @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).
* @typeParam ResultDate - The result `Date` type, it is the type returned from the context function if it is passed, or inferred from the arguments.
*
* @param date - The date to be changed
* @param amount - The amount of days to be added.
* @param options - An object with options
*
* @returns The new date with the days added
*
* @example
* // Add 10 days to 1 September 2014:
* const result = addDays(new Date(2014, 8, 1), 10)
* //=> Thu Sep 11 2014 00:00:00
*/
export function addDays<
DateType extends Date,
ResultDate extends Date = DateType,
>(
date: DateArg<DateType>,
amount: number,
options?: AddDaysOptions<ResultDate> | undefined,
): ResultDate {
const _date = toDate(date, options?.in);
if (isNaN(amount)) return constructFrom(options?.in || date, NaN);
// If 0 days, no-op to avoid changing times in the hour before end of DST
if (!amount) return _date;
_date.setDate(_date.getDate() + amount);
return _date;
}