JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <body>
        <h1>Validation Example</h1><br />
        <h2>Insert just 1 digit<h2>
        <form id="form" onsubmit="return false">
            <label>Input
                <input type="text" pattern="[0-9]" id="input"/></label> 
                <input type="submit" class="hide" id="inputButton">         
        </form>
    </body>
</html>

CSS

.hide {
visibility: hidden;
}

JavaScript

var input = document.getElementById("input"),
    inputButton =  document.getElementById("inputButton")

    input.onkeyup=function () {
        inputButton.click();        
    }