index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
    <form name="publish">
        <input type="text" name="message">
        <input type="submit" value="Send">
    </form>

    <ul id="messages">

    </ul>

<script>
    publish.onsubmit = function () {
        console.log(this.elements.message.value);
        var xhr = new XMLHttpRequest();
        xhr.open("POST", "/publish", true);
        xhr.send(JSON.stringify({message: this.elements.message.value}));
        this.elements.message.value = "";
        return false;

    };

    subscribe();

    function subscribe () {
        var xhr = new XMLHttpRequest();
        xhr.open("GET", "/subscribe", true);
        xhr.onload = function () {
            var li = document.createElement("li");
            li.textContent = this.responseText;
            messages.appendChild(li);
            subscribe()
        };
        xhr.send("");
    }


</script>

</body>

</html>