Client: postMessage() method
The postMessage()
method of the
Client
interface allows a service worker to send a message to a client
(a Window
, Worker
, or SharedWorker
). The
message is received in the "message
" event on
navigator.serviceWorker
.
Syntax
js
postMessage(message)
postMessage(message, transferables)
Parameters
message
-
The message to send to the client. This can be any structured-cloneable type.
transferables
Optional-
A sequence of objects that are transferred with the message. The ownership of these objects is given to the destination side and they are no longer usable on the sending side.
Return value
None (undefined
).
Examples
Sending a message from a service worker to a client:
js
addEventListener("fetch", (event) => {
event.waitUntil(
(async () => {
// Exit early if we don't have access to the client.
// Eg, if it's cross-origin.
if (!event.clientId) return;
// Get the client.
const client = await clients.get(event.clientId);
// Exit early if we don't get the client.
// Eg, if it closed.
if (!client) return;
// Send a message to the client.
client.postMessage({
msg: "Hey I just got a fetch from you!",
url: event.request.url,
});
})()
);
});
Receiving that message:
js
navigator.serviceWorker.addEventListener("message", (event) => {
console.log(event.data.msg, event.data.url);
});
Specifications
Specification |
---|
Service Workers # dom-client-postmessage-message-options |
Browser compatibility
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