https://www.ard-text.de/static/js/num.js?d=1

1function fnAddEvent(n, e, t) {
2    n.addEventListener ? n.addEventListener(e, t, !1) : n.attachEvent && (n["e" + e + t] = t, n[e + t] = function() {
3        n["e" + e + t](window.event)
4    }, n.attachEvent("on" + e, n[e + t]))
5}
6
7function fnValidate(n, e) {
8    var t = n.value.match(/^([1-8]{1}\d{2}){1}$/) ? !0 : !1;
9    return n.setCustomValidity && n.setCustomValidity(t ? "" : e), t
10}
11
12function fnCheckInput(n) {
13    console.log("CHIN");
14    var e = document.getElementById("id"),
15        t = e ? fnValidate(e, n) : !1;
16    return t || (e.value = ""), t
17}
18
19function fnSubmit(n, e) {
20    var t = !1;
21    return 3 == n.value.length && (t = fnValidate(n, e), t ? window.location.href = "/mobil/" + n.value : (document.getElementById("ok").click(), n.value = "")), t
22}
23
24function fnInit(n) {
25    var e = document.getElementById("id");
26    console.log(e), e && (e.value = "", fnAddEvent(e, "focus", function() {
27        return e.value = "", !0
28    }), fnAddEvent(e, "keydown", function(e) {
29        var t = !1;
30        return e.keyCode == VK_ENTER && (t = fnCheckInput(n)), t
31    }), fnAddEvent(e, "keyup", function() {
32        fnSubmit(e, n)
33    }))
34}
35if ("undefined" != typeof KeyEvent && "undefined" != typeof KeyEvent.VK_ENTER) var VK_ENTER = KeyEvent.VK_ENTER;
36if ("undefined" == typeof VK_ENTER) var VK_ENTER = 13;
37var MsgValidity = "Bitte geben Sie eine dreistellige Zahl von 100 bis 899 ein.";
38window.addEventListener ? window.addEventListener("load", fnInit(MsgValidity), !1) : window.attachEvent ? window.attachEvent("onload", fnInit(MsgValidity)) : window.onload = fnInit(MsgValidity);