Вот мое решение
<input type="tel" name="phone" maxlength="16" placeholder="+7(___)___-__-__" id="phone"/>
<input type="tel" name="phone" maxlength="16" placeholder="+7(___)___-__-__" id="phone2"/>
//------------javaScript--------------------------------
//подключение к текстовому полю
document.querySelector('#phone').onkeydown = function(e){
inputphone(e,document.querySelector('#phone'))
}
document.querySelector('#phone2').onkeydown = function(e){
inputphone(e,document.querySelector('#phone2'))
}
//-- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --
//Функция маски формат +7 (
function inputphone(e, phone){
function stop(evt) {
evt.preventDefault();
}
let key = e.key, v = phone.value; not = key.replace(/([0-9])/, 1)
if(not == 1 || 'Backspace' === not){
if('Backspace' != not){
if(v.length < 3 || v ===''){phone.value= '+7('}
if(v.length === 6){phone.value= v +')'}
if(v.length === 10){phone.value= v +'-'}
if(v.length === 13){phone.value= v +'-'}
}
}else{stop(e)} }