isDate

Checks whether a value is a valid Date instance.

This helper verifies two things:

1. The value is actually a Date object (instanceof Date).
2. The internal timestamp is valid (getTime() is not NaN).

It never throws and never mutates input.

Signature

function isDate(value: unknown): value is Date

Name	Data type	Description
value	unknown	The value to check. Must be a Date instance with a valid timestamp to return true.

Returns

A boolean:

• true: If the value is a Date instance and its timestamp is valid.
• false: Otherwise.

Examples

isDate(new Date())                 // true
isDate(new Date("2020-01-01"))     // true

isDate(new Date("invalid"))        // false
isDate(Date.now())                 // false
isDate("2020-01-01")               // false
isDate(null)                       // false
isDate({})                         // false

Notes

• Invalid Date objects such as new Date("invalid") are rejected because their time value is NaN.
• This helper does not attempt to parse or coerce values into dates.
• Use normalizeDate if you need to convert values into Date instances.
• Use validateDate if you need a Result<T> instead of a boolean.

Next up

isEnumValue