JSFiddle - React, Tailwind, and code Playground

HTML

<form name = "RegForm" class="login">
       <input type="text" name="username" id="username" placeholder="Enter your username">
</form>

JavaScript

userID_textfield.onkeydown = function(e) {   
        var prohibited = "!@#$%^&*()+=;:`~\|'?/.><, \"";
        var prohibitedchars = prohibited.split("");
        var prohibitedcharcodes = new Array();
    
        for (var i = 0; i < prohibitedchars.length + 1; i++) {
            prohibitedcharcodes.push(prohibitedchars[i].charCodeAt(i));
            for (var a = 0; a < prohibitedcharcodes.length + 1; a++) {
                if (prohibitedcharcodes[a] === e.which) {
                    return false;
                }
                else {
                    return true;
                }
            }
        }
    }