JSFiddle - React, Tailwind, and code Playground

HTML

<form class="ajax_form" action="ajax_mail.php" method="get">
    <h2>Связаться с нами</h2>
    <label>
        <span>Ваше имя:</span>
        <input type="text" name="uname" required/>
    </label>
    <label>
        <span>Ваш телефон:</span>
        <input type="text" name="phone" required/>
        <input type="text" name="email" placeholder="mail" required/>
    </label>
    <label>
        <span>Ваш город:</span>
        <select name="city">
            <option>Москва</option>
            <option>С-Петербург</option>
        </select>
    </label>
    <div class="button_wrap">
        <button class="button btn_green" type="submit">Отправить заявку</button>
    </div>
</form>

JavaScript

$(".ajax_form").on('submit', function(e) {
    var formData = $(".ajax_form").serialize();
    e.preventDefault();
    $.ajax({
        type: "GET",
        url: "/echo/html/",
        dataType: 'json',
        data: formData
    }).done(function() {
        alert("Спасибо за заявку!");
    });
});