Choosing a date using date field and then wanting that to populate another field with day of week?

Hi. I'm creating a fillable form and I'd like to allow the user to pick a date using the date field which will then auto-populate a field next to it with the corresponding day of the week. I tried to do a custom format in the properties which seemed to work fine on my computer but would error when filling it using an iPad. (Form will most of the time be filled out on an iPad).

I've been searching forums and other pages for an answer however I have absolutley no JavaScript experience. I'm also finding it a little hard to get started on my own. Any assistance would be great or referral to an appropriate resource. Thank you so much.