Apple Watch compared to Fitbit Ionic

I have used Fitbit produces for about the last year; including a Fitbit Ionic for about 15 months; but recently the Ionic failed and there is no fix. I am looking at an Apple watch as a replacement, but I do no see that there is a sleep tracking function and I really like this function. Can someone tell me if Apple Watches have a sleep tracking app. Also, does the Apple watch have an alarm clock function. I like the vibrating alarm of the Ionic and it will work even when my phone is turned off; can an Apple watch do the same?

Thanks!