Chrome Extension - tabId and tabIndex undefined - google-chrome-extension

Question

I am creating a Chrome Extension. When I try to get the tabId and tabIndex, they are both showing as "undefined".
here is the background.js:
chrome.extension.onRequest.addListener(
function (request, sender)
{
if (request.command == "selected-tab")
{
chrome.tabs.getSelected(null,
function()
{
// both show as undefined
alert('sender.tabId: ' + sender.tabId);
alert('sender.tabIndex' + sender.tabIndex);
});
}
}
);
Here is the content-script.js:
chrome.extension.sendRequest({ command: "selected-tab", urltext: urlText });
Here is the manifest.json:
{
"manifest_version": 2,
"name": "test2",
"description": "Test2 desc",
"version": "1.0",
"permissions": [
"tabs", "http://*/*", "https://*/*","contextMenus"
],
"background": {
"scripts": ["jquery-1.11.0.min.js", "background.js"]
},
"content_scripts": [
{
"matches": ["http://*/*"],
"js": ["jquery-1.11.0.min.js", "content-script.js"]
}
]
}
How can I get the tabId and tabIndex of the current tab inside background.js?
Thanks Before Hand
Update #1
Tried this inside background.js and it still did not show the tab id on the alert:
chrome.tabs.getCurrent(function (tab) {
alert(tab.id);
});

Answer 1

The chrome.extension.onRequest event supports the concept of a response back to the sender, but if the receiver doesn't reply (or indicate that it intends to) there is some code that tries to garbage collect the JS context setup inside your event handler. Because you're starting another asynchronous operation via chrome.tabs.getSelected inside the context of your handler, it might be that the garbage collection kicks in before your callback for getSelected fires.
See the documentaiton on the callback parameter to runtime.onMessage:
"Function to call (at most once) when you have a response. The
argument should be any JSON-ifiable object. If you have more than one
onMessage listener in the same document, then only one may send a
response. This function becomes invalid when the event listener
returns, unless you return true from the event listener to indicate
you wish to send a response asynchronously (this will keep the message
channel open to the other end until sendResponse is called)."
One easy fix to try would be to manually call sendResponse inside your getSelected callback:
chrome.extension.onRequest.addListener(
function (request, sender)
{
if (request.command == "selected-tab")
{
chrome.tabs.getSelected(null,
function()
{
// both show as undefined
alert('sender.tabId: ' + sender.tabId);
alert('sender.tabIndex' + sender.tabIndex);
sendResponse(); // context can now be GC'd
});
}
return true; // indicates we plan to call sendResponse
}
);