JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <textarea id="textarea" rows="4" cols="50" onKeyPress="validate(event)" onPaste="validatepaste(event)"></textarea>
</div>

JavaScript

function validatepaste(e) {
    //var ctrldown =  e.ctrlKey ? e.ctrlKey : ((e.keyCode === 17) ? true : false);
    var pastedata = e.clipboardData.getData('text/plain');
    if (isNaN(pastedata)) {
        e.preventDefault();
        console.log("PASTE FAIL!");
        console.log(pastedata);
        return false;
    } else {
            console.log("PASTE!");
            console.log(pastedata); 
    }
}

function validate(e) {
    //getting key code of pressed key
    var keycode = (e.which) ? e.which : e.keyCode;
    var phn = document.getElementById('textarea');
    //comparing pressed keycodes
    if ((keycode < 48 || keycode > 57) && keycode !== 13) {
        e.preventDefault();
        console.log("FAIL");
        return false;
    } else {
        console.log("OK!");
    }
}