Disallow anything matching the regex pattern

HTML

<input class="valid-char" id="b" style="width:300px" placeholder="keypress">
<div class="counter-a"></div>
<div class="key-a"></div>
<div class="arabic-a"></div>
<div class="russian-a"></div>

JavaScript

var counterA = 0;

//$(".valid-char-a").keypress(function (e) {
var checkChar = function(v) {

    $("div.counter-a").text("counter: "+ ++counterA);
    
    // Disallow anything matching the regex pattern
    // For more on JavaScript Regular Expressions, look here: https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Regular_Expressions

    var cyrillicAlphabet = /[\u0400-\u04ff]|[\u0500-\u052f]|[\u2de0-\u2dff]|[\ua640-\ua69f]|[\u1d2b-\u1d78]/g;
    var arabicAlphabet = /[\u0600-\u06ff]|[\u0750-\u077f]|[\ufb50-\ufc3f]|[\ufe70-\ufefc]/g;

    
    // Retrieving the key from the char code passed in event.which
    // For more info on even.which, look here: http://stackoverflow.com/q/3050984/114029
    
    //e = e || window.event;
    //var k = e.keyCode || e.which;
    //var key = String.fromCharCode(k);
    var key  = v;
    
    
    $("div.key-a").text("key: "+key);
    var ruChar = cyrillicAlphabet.test(key);
    var arChar = arabicAlphabet.test(key);

    $("div.arabic-a").text("arabic: "+arChar);
    $("div.russian-a").text("russian: "+ruChar);

    // For the keyCodes, look here: http://stackoverflow.com/a/3781360/114029     
    if (ruChar || arChar) {
        //document.getElementById("b").value.substring(this.value.length-1);
//x[i].value.substring(x[i].value.length-1);
        alert("STOP! - Please enter your details in english");
        return false;
    } 
    
};

var handler = function() {
    //var char = this.value.substring(this.value.length-1);    
    var char = this.value.slice(-1);
    checkChar(char);
};

var x = document.getElementsByClassName("valid-char");
var i;
for (i = 0; i < x.length; i++) {
    x[i].oninput = handler;
}