JSFiddle - React, Tailwind, and code Playground

HTML

<input id="seq" value="123456789" max=999999999 min=100000000 type=number onchange="humannum()" />
<button onclick="randnum()">rand</button>
<input id="res" value="">

JavaScript

function humannum() {
    var num9 = $('#seq').val();
    if (num9.length != 9) {
        $('#res').val('wrong num');
        return;
    }
    var k1 = [4, 8, 7, 4, 11, 9, 5, 3, 8];
    var k2 = [2, 4, 8, 7, 4, 11, 9, 5, 3, 8];
    var num10 = calk(num9, k1);
    var num11 = calk(num9 + '' + num10, k2);
    $('#res').val(num9 + '' + num10 + '' + num11);
}

function calk(num, k) {
    var n = [];
    var x = [];
    for (var i = 0; i < num.length; i++) {
        n[i] = parseInt(num[i])
        x[i] = parseInt(num[i]) * parseInt(k[i]);
    }
    var sx = x.reduce((accumulator, currentValue) => {
        return accumulator + currentValue
    });
    var mod = parseInt(sx) % 11;
    var preres = 11 - mod;
    var res = preres;
    if (preres >= 10) {
        res = 0;
    }
    return res;
}

function randnum() {
    var y = '';
    for (var a = 1; a <= 9; a++) {
        var x = Math.floor(Math.random() * 9);
        y += '' + x;
    }
    $('#seq').val(y).change();
}