Auto formatting phone number to 123.456.7890

Hi All,

My requirement is to format the user entered phone number to this format 123.456.7890

If the user enters numbers less than 10, I have to show a validation message.

I am new to CRM and javascript. I have done some R & D but this type of formatting. havent found.

Any help for this code  and steps doing this will be very helpful to me.