Make a connection between different contexts inside the extension.

You can call this:

  • in an extension's content scripts, to establish a connection with the extension's background scripts (or similarly privileged scripts, like popup scripts or options page scripts).
  • in an extension's background scripts (or similarly privileged scripts), to establish a connection with a different extension.

Note that you can't use this function to connect an extension to its content scripts. To do this, use tabs.connect().

By default, this connection enables the extension to exchange messages with itself or any other extension (if extensionId is specified). However, the externally_connectable manifest key can be used to limit communication to specific extensions and enable communication with websites. Connections within the extension trigger the runtime.onConnect event, connections from other extensions or web pages trigger the runtime.onConnectExternal event.


let port = browser.runtime.connect(
  extensionId, // optional string
  connectInfo  // optional object


extensionId Optional

string. The ID of the extension to connect to. If the target has set an ID explicitly using the browser_specific_settings key in manifest.json, then extensionId should have that value. Otherwise it should have the ID that was generated for the target.

connectInfo Optional

object. Details of the connection:

name Optional

string. Will be passed into runtime.onConnect for processes that are listening for the connection event.

includeTlsChannelId Optional

boolean. Whether the TLS channel ID will be passed into runtime.onConnectExternal for processes that are listening for the connection event.

Return value

runtime.Port. Port through which messages can be sent and received. The port's onDisconnect event is fired if the extension does not exist.

Browser compatibility

BCD tables only load in the browser


This content script:

  • connects to the background script and stores the Port in a variable called myPort.
  • listens for messages on myPort and logs them.
  • sends messages to the background script, using myPort, when the user clicks the document.
// 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: ");

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.
  • sends messages to the content script, using portFromCS, when the user clicks the extension's browser action.
// 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");


browser.browserAction.onClicked.addListener(() => {
  portFromCS.postMessage({ greeting: "they clicked the button!" });

Note: This API is based on Chromium's chrome.runtime API. This documentation is derived from runtime.json in the Chromium code.