browser.runtime.onConnect.addListener(listener)browser.runtime.onConnect.removeListener(listener)browser.runtime.onConnect.hasListener(listener)

Events have three functions:

addListener(listener)

Adds a listener to this event.

removeListener(listener)

Stop listening to this event. Thelistener argument is the listener to remove.

hasListener(listener)

Checks whether alistener is registered for this event. Returnstrue if it is listening,false otherwise.

function

The function called when this event occurs. The function is passed this argument:

port

Aruntime.Port object connecting the current script to the other context it is connecting to.

This content script:

• connects to the background script, and stores thePort in a variablemyPort
• listens for messages onmyPort, and logs them
• sends messages to the background script, usingmyPort, when the user clicks the document

// content-script.jslet 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 namedportFromCS
  • 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, usingportFromCS, when the user clicks the extension's browser action

// background-script.jslet 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!" });});