var data = require('sdk/self').data;
var tabs = require('sdk/tabs');

var alertContentScript = "self.port.on('alert', function(message) {" +
                         "  window.alert(message);" +
                         "})";

tabs.on("ready", function(tab){
    if (tab.url.indexOf('ya.ru')>0) {
        
        worker = tab.attach({
            contentScript: alertContentScript
        });
        tab.port.on("myEvent", function(text) {
            worker.port.emit("alert", text);
        });
        tab.attach({
            contentScript: "self.port.emit('myEvent', 'test text');"
        });
    }
});