Consume SSE in client

stream.js

function appendChat(chat) { ... }

function sendChat() {
    event.preventDefault();

    const chatForm = document.getElementById("chat-form");
    const chatMessage = chatForm.elements.message.value;

    const xhr = new XMLHttpRequest();
    xhr.open('POST', 'chat');
    xhr.setRequestHeader('Content-Type', 'application/json');
    xhr.onload = function () {
        if (xhr.status === 201) {
            chatForm.elements.message.value = "";
        }
    };
    xhr.send(JSON.stringify({
        user: currentUser,
        message: chatMessage
    }));
}

const source = new EventSource("{{ url_for('sse.stream') }}");
source.addEventListener('chat', function (event) {
    const chat = JSON.parse(event.data);
    appendChat(chat)
}, false);