JSFiddle - React, Tailwind, and code Playground

HTML

<h2>1</h2>
<input type="number" value="-1">
<button>Change</button>

JavaScript

$('button').on('click',function(){
    var val = $('input').val();
        val = parseInt(val);
    var current = $('h2').html();
        current = parseInt(current);
    $('h2').html(val);
    
    var val_test,current_test;
    if(val<0) {
        val_test = 'negative';
    } else {
        val_test = 'positive';
    }
    if(current<0) {
        current_test = 'negative';
    } else {
        current_test = 'positive';
    }
    
    if(current_test!==val_test) {
        alert('Yeah!');
    }
});