JSFiddle - React, Tailwind, and code Playground

by Denis Ineshin

HTML

<input class="login" name="login" />
<button class="submit" disabled>Войти</button>

CSS

button[disabled] {
    opacity: 0.3;
}

JavaScript

$('document').ready(function(){
    var $login = $(".login"),
        $button = $(".submit");
    
    var check = function (text) {
        if (text.length > 3) {
            $button.prop("disabled", false);
        } else {
            $button.prop("disabled", true);
        }
    };
    
    $login.on("keyup", function () {
        var val = $(this).prop("value");
        check(val);
    });
});