how to send message from backgroundjs to content script in chrome extension?

Question

I am working on chrome extension and I've stuck on a very specific part where backgroundjs is suppose to send a message to current active tab .

This is my manifest file

manifest.json

{
     "manifest_version": 2,
     "name": "test",
     "description": "Some_Test",
     "version": "1.0",

     "background": {
     "page":  "background.html"
     },
     "content_scripts": [
         {
             "matches": [ "http://*/*", "https://*/*" ],
             "js": [ "content.js" ]
         }
     ],
     "permissions": [
     "background",
     "activeTab",
     "tabs",
     "http://*/*",
     "https://*/*"
     ],
     "browser_action": {
         "default_popup": "popup.html"
      }
}

popup.html

<html>
<body>
    <button id="read-button">Read</button>
    <script type="text/javascript" src="popup.js"></script>
</body>
</html>

popup.js

function readObject(e) {
    console.log(chrome.extension.getBackgroundPage().read());
}

document.getElementById('read-button').addEventListener('click', readObject);

background.html

<!DOCTYPE html>
<html>
    <head>
    </head>
<body>
    <script type="text/javascript" src="background.js"></script>
</body>
</html>

background.js

function read() {
    chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) {
        chrome.tabs.sendMessage(tabs[0].id, { greeting: "hello" }, function (response) {
            return response.farewell;
        });
    });
}

content.js

chrome.runtime.onMessage.addListener(
  function (request, sender, sendResponse) {
      console.log("hello");
      if (request.greeting == "hello")
          sendResponse({ farewell: "goodbye" });
  });

This is where the error is :

chrome.tabs.sendMessage(tabs[0].id, { greeting: "hello" }, function (response) {
            return response.farewell;
        });

It seems that I cannot access tabs[0] object or I am unable to understand the Array which it returns, because i want to access the active tab and tabs[0] simply means it is getting the first tab in the browser and not the active tab.

woxxom · Accepted Answer · 2015-11-06 09:25:35Z

1

I think this can only happen if the active window is the Developer Tools of the background page.

Just switch to a normal browser window when testing the extension or define read() function in popup.js and remove the background page altogether if it's not absolutely needed.

answered Nov 6, 2015 at 9:25

woxxom

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