JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="text" name="quantity" id="quantity" value="1" />
</form>

<div id="result"></div>

CSS

body,input { font:14px/22px Arial,Verdana,sans-serif; color:#000; padding:.5em; }
div,form { margin:20px; }
input { outline:none; border:1px solid #eee; width:75px; text-align:center; }

JavaScript

$(document).ready(function(){
    test();
});

function test()
{
    $('#quantity').keyup(function(){
        var quantity = $('input:text#quantity').val();
        if(isInteger(quantity))
        {
            var msg = false;
            if(quantity > 1)
            {
                msg = true;
            }
            
            // more code . . .
            
            if(msg === true)
            {
                 $('#result').html(quantity+' items');   
            }
            else
            {
                $('#result').hide();
            }
        }
    });
}
                         
function isInteger(value) {
    return /^[0-9]+$/.test(value);
}