BroadcastChannel: message イベント

<h1>Sender</h1>
<label for="message">Type a message to broadcast:</label><br/>
<textarea id="message" name="message" rows="1" cols="40">Hello</textarea>
<button id="broadcast-message" type="button">Broadcast message</button>

body {
     border: 1px solid black;
     padding: .5rem;
     height: 150px;
     font-family: "Fira Sans", sans-serif;
}

h1 {
    font: 1.6em "Fira Sans", sans-serif;
    margin-bottom: 1rem;
}

textarea {
    padding: .2rem;
}

label, br {
    margin: .5rem 0;
}

button {
    vertical-align: top;
    height: 1.5rem;
}

const channel = new BroadcastChannel('example-channel');
const messageControl = document.querySelector('#message');
const broadcastMessageButton = document.querySelector('#broadcast-message');

broadcastMessageButton.addEventListener('click', () => {
    channel.postMessage(messageControl.value);
})

<h1>Receiver 1</h1>
<div id="received"></div>

body {
    border: 1px solid black;
    padding: .5rem;
    height: 100px;
    font-family: "Fira Sans", sans-serif;
}

h1 {
    font: 1.6em "Fira Sans",
    sans-serif; margin-bottom: 1rem;
}

const channel = new BroadcastChannel('example-channel');
channel.addEventListener('message', (event) => {
  received.textContent = event.data;
});

<h1>Receiver 2</h1>
<div id="received"></div>

body {
    border: 1px solid black;
    padding: .5rem;
    height: 100px;
    font-family: "Fira Sans", sans-serif;
}

h1 {
    font: 1.6em "Fira Sans", sans-serif;
    margin-bottom: 1rem;
}

const channel = new BroadcastChannel('example-channel');
channel.addEventListener('message', (event) => {
  received.textContent = event.data;
});