Obtaining "this" tab ID from content script in Chrome extension?

From a content script, is it possible to access that tab's id?

I want to send a message to the background page from the content script that tells my extension to "do something with this tab" using the chrome.tabs.* API.

A tabID is needed, and there is no point in doing a bunch of logic in the background page to hunt for a tabID when my content script can simply tell it the tabID in the message contents.

Tab id is automatically passed inside MessageSender object:

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
	console.log("sent from tab.id=", sender.tab.id);
});

If you want the tabId of yourself (in my case in Content Script) without requiring "tabs" permission, a workaround is to have Content Script send a dummy message to the background script, then have background script respond with sender.tab.id back to the Content Script!

e.g. in content.js:

chrome.runtime.sendMessage({ text: "what is my tab_id?" }, tabId => {
   console.log('My tabId is', tabId);
});

and in background.js:

chrome.runtime.onMessage.addListener(function(msg, sender, sendResponse) {
    if (msg.text == "what is my tab_id?") {
        sendResponse({tab: sender.tab.id});
     }
});

it's a stupid workaround that worked for me. :)

PS. Oh, if you have tabs permission then you can run this async query very easily:

chrome.tabs.query({active: true, currentWindow: true}, function(tabs){
    var myTabId = tabs[0].id;
    chrome.tabs.sendMessage(myTabId, {text: "hi"}, function(response) {
        alert(response);
    });
});

If you're using Ports for two-way long-lived connections, the second argument in the callback is a Port object, so to access the tab ID is then:

chrome.runtime.onConnect.addListener(port => {
  if (port.name === "foo") {
	port.onMessage.addListener((msg, sendingPort) => {
	  console.log("sent from tab.id=", sendingPort.sender.tab.id);
    });
  }
});

If a content script is injected programmatically, another approach is to store tabId in a global variable:

const injectTabId = (callback) => chrome.tabs.executeScript(
  tabId,
  {code: `window.tabId = ${tabId}`},
  callback
);

const injectFile = () => chrome.tabs.executeScript(
  tabId,
  {file: 'content.js'}
);

injectTabId(injectFile);

In the content script, access it with window.tabId. The variable won't be exposed to page scripts because of content scripts living in an isolated world.

Correction of the selected answer for nowadays:

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
    console.log("sent from tab.id=", sender.id);
});