How to send message from panel to page-mod's content script directly?

Question

If there is a code snippet in Firefox addon like following:

var pagemod = PageMod({
    include: ['*'],
    contentScriptFile: [data.url('content.js')]
});

panel = require("sdk/panel").Panel({
  width: 322,
  height: 427,
  contentURL: data.url("main.html"),
  include:["http://*/*","https://*/*"],
  contentScriptFile: [data.url('panel.js')]  
});

I have found some example code in the Chrome extension. They use window.parent.postMessage(message, "*") to send message and use window.addEventListener("message",function (e) {//do something} to receive message. How can I send message from "panel.js" to "content.js" directly in the Firefox addon?

Answer 1

The concept of the solution is very similar to this answer:

1. Maintain a list of message ports for each tab.
2. Whenever you want to send a message, send a message to all listed ports.

The following code is used to maintain a list of ports:

var ports = [];
var pagemod = PageMod({
    include: ['*'],
    contentScriptFile: [data.url('content.js')],
    onAttach: function(worker) {
        ports.push(worker.port);
        worker.on('detach', function() {
            var index = ports.indexOf(worker.port);
            if (index !== -1) ports.splice(index, 1);
        });
    }
});

Now, whenever you want to send a message from panel.js, just use:

// panel.js
self.port.emit('message-to-tabs', 'example of message');

The message has to be handled in the main script, after creation of the panel:

panel = require('sdk/panel').Panel({
    width: 322,
    height: 427,
    contentURL: data.url('main.html'),
    include: ['http://*/*', 'https://*/*'],
    contentScriptFile: [data.url('panel.js')]  
});
panel.port.on('message-to-tabs', function(message) {
    for (var i=0; i<ports.length; i++) {
        ports[i].emit('message-to-tab', message);
    }
});

In the tab's content script (content.js), you can listen to this event and handle it as follows:

self.port.on('message-to-tab', function(message) {
    // Do something with message
});