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isDate ​

The isDate utility is a type guard that checks if a given value is a valid JavaScript Date object.

Implementation ​

View Source Code
ts
/**
 * Determines if the passed value is a valid Date Object.
 *
 * @example
 * ```ts
 * isDate(new Date()); // true
 * isDate(123); // false
 * ```
 *
 * @param arg - The argument to be checked.
 *
 * @returns `true` if the value is a valid Date object, else `false`.
 */
export function isDate(arg: unknown): arg is Date {
  return arg instanceof Date && !Number.isNaN(arg.getTime());
}

export const IS_DATE_ERROR_MSG = 'Expected a Date object';

Features ​

  • Isomorphic: Works in both Browser and Node.js.
  • Type Guard: Automatically narrows types to Date within conditional blocks.
  • Strict Check: Only returns true for actual Date instances that are also valid (not "Invalid Date").

API ​

ts
function isDate(value: unknown): value is Date;

Parameters ​

  • value: The value to check.

Returns ​

  • true if the value is a valid Date object; otherwise, false.

Examples ​

Basic Usage ​

ts
import { isDate } from '@vielzeug/toolkit';

isDate(new Date()); // true
isDate(new Date('abc')); // false (Invalid Date)
isDate('2024-01-01'); // false (String, not Date object)
isDate(Date.now()); // false (Number, not Date object)

Type Guarding ​

ts
import { isDate } from '@vielzeug/toolkit';

function format(val: unknown) {
  if (isDate(val)) {
    // val is narrowed to Date
    return val.toISOString();
  }
}

Implementation Notes ​

  • Returns true if value instanceof Date and !isNaN(value.getTime()).
  • Throws nothing; safe for any input type.

See Also ​