runtime.Port
A Port
object represents one end of a connection between two specific contexts, which can be used to exchange messages.
One side initiates the connection, using a connect()
API. This returns a Port
object. The other side listens for connection attempts using an onConnect
listener. This is passed a corresponding Port
object.
Once both sides have Port
objects, they can exchange messages using Port.postMessage()
and Port.onMessage
. When they are finished, either end can disconnect using Port.disconnect()
, which will generate a Port.onDisconnect
event at the other end, enabling the other end to do any cleanup required.
A Port
can also become disconnected in response to various events. See Lifecycle.
You can use this pattern to communicate between:
- different parts of your extension (for example, between content scripts and background scripts)
- between your extension and a native application running on the user's computer.
- between your extension and a different extension
You need to use different connection APIs for different sorts of connections, as detailed in the table below.
Connection type | Initiate connection attempt | Handle connection attempt |
---|---|---|
Background script to content script | tabs.connect() |
runtime.onConnect |
Content script to background script | runtime.connect() |
runtime.onConnect |
Extension to native application | runtime.connectNative() |
Not applicable (see Native messaging). |
Extension to Extension | runtime.connect() |
runtime.onConnectExternal |
Type
Values of this type are objects. They contain the following properties:
name
-
string
. The port's name, defined in theruntime.connect()
ortabs.connect()
call that created it. If this port is connected to a native application, its name is the name of the native application. disconnect
-
function
. Disconnects a port. Either end can call this when they have finished with the port. It will causeonDisconnect
to be fired at the other end. This is useful if the other end is maintaining some state relating to this port, which can be cleaned up on disconnect. If this port is connected to a native application, this function will close the native application. error
-
object
. If the port was disconnected due to an error, this will be set to an object with a string propertymessage
, giving you more information about the error. SeeonDisconnect
. onDisconnect
-
object
. This contains theaddListener()
andremoveListener()
functions common to all events for extensions built using WebExtension APIs. Listener functions will be called when the other end has calledPort.disconnect()
. This event will only be fired once for each port. The listener function will be passed thePort
object. If the port was disconnected due to an error, then thePort
argument will contain anerror
property giving more information about the error:js
port.onDisconnect.addListener((p) => { if (p.error) { console.log(`Disconnected due to an error: ${p.error.message}`); } });
Note that in Google Chrome
port.error
is not supported: instead, useruntime.lastError
to get the error message. onMessage
-
object
. This contains theaddListener()
andremoveListener()
functions common to all events for extensions built using WebExtension APIs. Listener functions will be called when the other end has sent this port a message. The listener will be passed the value that the other end sent. postMessage
-
function
. Send a message to the other end. This takes one argument, which is a serializable value (see Data cloning algorithm) representing the message to send. It will be delivered to any script listening to the port'sonMessage
event, or to the native application if this port is connected to a native application. sender
Optional-
runtime.MessageSender
. Contains information about the sender of the message. This property will only be present on ports passed toonConnect
/onConnectExternal
listeners.
Lifecycle
The lifecycle of a Port
is described in the Chrome docs.
There is, however, one important difference between Firefox and Chrome, stemming from the fact that the runtime.connect
and tabs.connect
APIs are broadcast channels. This means that there may be potentially more than one recipient, and this results in ambiguity when one of the contexts with a runtime.onConnect
call is closed. In Chrome, a port stays active as long as there is any other recipient. In Firefox, the port closes when any of the contexts unloads. In other words, the disconnection condition,
- All frames that received the port (via
runtime.onConnect
) have unloaded.
which holds in Chrome, is replaced by
- Any frame that received the port (via
runtime.onConnect
) has unloaded.
in Firefox (see bug 1465514).
Browser compatibility
BCD tables only load in the browser
Examples
Connecting from content scripts
This content script:
- connects to the background script and stores the
Port
in a variable calledmyPort
. - listens for messages on
myPort
and logs them. - sends messages to the background script, using
myPort
, when the user clicks the document.
js
// content-script.js
let myPort = browser.runtime.connect({name:"port-from-cs"});
myPort.postMessage({greeting: "hello from content script"});
myPort.onMessage.addListener((m) => {
console.log("In content script, received message from background script: ");
console.log(m.greeting);
});
document.body.addEventListener("click", () => {
myPort.postMessage({greeting: "they clicked the page!"});
});
The corresponding background script:
- listens for connection attempts from the content script.
- when it receives a connection attempt:
- stores the port in a variable named
portFromCS
. - sends the content script a message using the port.
- starts listening to messages received on the port, and logs them.
- stores the port in a variable named
- sends messages to the content script, using
portFromCS
, when the user clicks the extension's browser action.
js
// background-script.js
let portFromCS;
function connected(p) {
portFromCS = p;
portFromCS.postMessage({greeting: "hi there content script!"});
portFromCS.onMessage.addListener((m) => {
console.log("In background script, received message from content script")
console.log(m.greeting);
});
}
browser.runtime.onConnect.addListener(connected);
browser.browserAction.onClicked.addListener(() => {
portFromCS.postMessage({greeting: "they clicked the button!"});
});
Multiple content scripts
If you have multiple content scripts communicating at the same time, you might want to store each connection in an array.
js
// background-script.js
let ports = []
function connected(p) {
ports[p.sender.tab.id] = p
// …
}
browser.runtime.onConnect.addListener(connected)
browser.browserAction.onClicked.addListener(() => {
ports.forEach((p) => {
p.postMessage({greeting: "they clicked the button!"})
})
});
Connecting to native applications
This example connects to the native application "ping_pong" and starts listening for messages from it. It also sends the native application a message when the user clicks a browser action icon:
js
/*
On startup, connect to the "ping_pong" app.
*/
let port = browser.runtime.connectNative("ping_pong");
/*
Listen for messages from the app.
*/
port.onMessage.addListener((response) => {
console.log(`Received: ${response}`);
});
/*
On a click on the browser action, send the app a message.
*/
browser.browserAction.onClicked.addListener(() => {
console.log("Sending: ping");
port.postMessage("ping");
});
Note: This API is based on Chromium's chrome.runtime
API. This documentation is derived from runtime.json
in the Chromium code.