JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post">
    <input class="input" type="text" name="do_kogo" id="odbiorca" size="25" />
    <input class="input" id="temat" type="text" name="temat" size="25" />
    <textarea id="tresc_area" cols="45" rows="10" ></textarea>
    <input onclick="Check()" id="send_submit" type="submit" value="Send" />
</form>
<script>
function Check() {
    alert($("#tresc_area").val());
    return false;
}
</script>