LADYX,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<input value="" id="tel"> <input value="" > <input value="">
<script>
window.addEventListener("DOMContentLoaded", function() {
var keyCode;
function mask(event) {
event.keyCode && (keyCode = event.keyCode);
var pos = this.selectionStart;
if (pos < 3) event.preventDefault();
var matrix = "+7 (___) ___ ____",
i = 0,
def = matrix.replace(/\D/g, ""),
val = this.value.replace(/\D/g, ""),
new_value = matrix.replace(/[_\d]/g, function(a) {
return i < val.length ? val.charAt(i++) || def.charAt(i) : a
});
i = new_value.indexOf("_");
if (i != -1) {
i < 5 && (i = 3);
new_value = new_value.slice(0, i)
}
var reg = matrix.substr(0, this.value.length).replace(/_+/g,
function(a) {
return "\\d{1," + a.length + "}"
}).replace(/[+()]/g, "\\$&");
reg = new RegExp("^" + reg + "$");
if (!reg.test(this.value) || this.value.length < 5 || keyCode > 47 && keyCode < 58) this.value = new_value;
if (event.type == "blur" && this.value.length < 5) this.value = ""
}
var input = document.querySelector("#tel");
input.addEventListener("input", mask, false);
input.addEventListener("focus", mask, false);
input.addEventListener("blur", mask, false);
input.addEventListener("keydown", mask, false)
});
</script>
</body>
</html>