Phone number input

allow + at the beginning
otherwise allow only numbers and spaces
add space after sequence of 3 numbers
minimize autospaces count
allow space after 1 or 2 numbers, too
replace sequence of spaces by single space
don't allow space after +
keep cursor position if replacement happens

Consider pattern attribute to enforce specific format on submit.

<input oninput="phone()" placeholder="Your phone number..."> <script> const phone = (e,o,p) => ( e=e||event, o=e.target, p=o.selectionStart, o.value = o.value .replace(/(^\+)|[^0-9 ]|\s+(?=\s)/g, '$1') .replace(/(\d)(\d{2})(?=\S)/g, (_,p1,p2,q) => p==q+1 ? p1+' '+p2 : (p++,p1+p2+' ')), e.inputType=="deleteContentBackward" && p && o.value[p-1]==' ' && p--, o.setSelectionRange(p,p) ) </script>