toISOString()

ES5+

Returns a string in ISO 8601 format (YYYY-MM-DDTHH:mm:ss.sssZ).

Syntax

date.toISOString()

Return Value

string

A string representing the date in ISO format

Examples

JavaScript

const date = new Date('2024-01-15T14:30:00');
console.log(date.toISOString());

Output:

// '2024-01-15T05:30:00.000Z'

📌 When to Use

Use toISOString() for API responses, database storage, logs, or any context requiring a standardized, timezone-neutral date format.

⚠️ Common Mistakes

Forgetting that toISOString() always returns UTC time (Z suffix), not local time.

Throwing an error on invalid Date - toISOString() throws RangeError for invalid dates.

✅ Best Practices

Always use toISOString() when sending dates to APIs or storing in databases for consistency.

Wrap in try-catch or validate the date first to handle potential RangeError.

⚡ Performance Notes

toISOString() involves string formatting which is slightly slower than getTime(), but still fast. Prefer caching if called repeatedly for the same date.

🌍 Real World Example

API Date Serialization

Format dates consistently for REST API requests and responses.

function createEventPayload(eventData) {
  const now = new Date();

  return {
    ...eventData,
    createdAt: now.toISOString(),
    updatedAt: now.toISOString(),
    scheduledFor: new Date(eventData.scheduledFor).toISOString(),
    metadata: {
      timezone: Intl.DateTimeFormat().resolvedOptions().timeZone,
      localTime: now.toLocaleString()
    }
  };
}

const payload = createEventPayload({
  title: 'Team Meeting',
  scheduledFor: '2024-03-20T14:00:00'
});

console.log(JSON.stringify(payload, null, 2));
// {
//   "title": "Team Meeting",
//   "createdAt": "2024-03-15T08:30:00.000Z",
//   "updatedAt": "2024-03-15T08:30:00.000Z",
//   "scheduledFor": "2024-03-20T14:00:00.000Z",
//   ...
// }

Related Methods

toLocaleString()