JSFiddle - React, Tailwind, and code Playground

HTML

Only valid content: <b>hello</b><br>
<input type="text" class="hello"/>
<button>Dummy</button>

JavaScript

$(function() {
    $('.hello').bind('focusout', function(e) {
        if(!isValid($(this).val())) {
            e.preventDefault();
            $(this).focus();
        }
    });
});
    
    function isValid(str) {
        if(str === "hello") {
            return true;
        } else {
            return false;
        }
    }