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title: toISOString()
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---

# toISOString()

Deprecated. Use `Date.toISOString()` instead.

## Signature

`toISOString(Date | T date)`

## Parameters

**_date_:** Type: `Date | T`. A `Date` object.

**_unit_:** Type: `string`. A datetime unit. Options are 'year', 'month', 'week', 'day', 'hour', 'minute', or 'second'.

## Returns

**Type: `Date`** An ISO8601 string.