Why doesn't toISOString include the offset?

[thj-dk]

Can you help me understand why dayjs().toISOString() doesn't include the offset by default?

Given the current behaviour, shouldn't this method be named ToUtcIsoString?
Or am I wrong, expecting this method to include the offset? What are the reasons behind this behavior?

I'm aware that I can get the ISO 8601 representation including offset using format(), but it's less obvious.

[dimarixsus]

I've always thought about this as just like JavaScript new Date().toISOString()