files/en-us/web/api/extendablemessageevent/ports/index.md
{{APIRef("Service Workers API")}}{{AvailableInWorkers("service")}}
The ports read-only property of the
{{domxref("ExtendableMessageEvent")}} interface returns the array containing the
{{domxref("MessagePort")}} objects representing the ports of the associated message
channel (the channel the message is being sent through.)
An array of {{domxref("MessagePort")}} objects.
When the following code is used inside a service worker to respond to a push messages
by sending the data received via {{domxref("PushMessageData")}} to the main context via
a channel message, the event
object of onmessage will be an ExtendableMessageEvent.
let port;
self.addEventListener("push", (e) => {
const obj = e.data.json();
if (obj.action === "subscribe" || obj.action === "unsubscribe") {
port.postMessage(obj);
} else if (obj.action === "init" || obj.action === "chatMsg") {
port.postMessage(obj);
}
});
self.onmessage = (e) => {
port = e.ports[0];
};
{{Specifications}}
{{Compat}}