Chrome Extension : Issue with SendMessage

Question

I am trying to change the contents of a page based on the output of a xhr call. I am sending a message from content.js making the xrh call in the background js file and then passing the output to content.js which alters the content of the page.

From my content.js file I am doing the following.

var s = document.createElement('script'); 
s.src = chrome.extension.getURL('src/content/main.js'); 
(document.head || document.documentElement).appendChild(s);

In my main.js I am doing

  chrome.runtime.sendMessage({
    method: 'GET',
    action: 'xhttp',
    url: myurl
  }, function(responseText) {
      console.log("Response Text is ", responseText);
  });

And in my bg.js I have the following

chrome.runtime.onMessage.addListener(function(request, sender, callback) {
    if (request.action == "xhttp") {
        var xhttp = new XMLHttpRequest();
        var method = request.method ? request.method.toUpperCase() : 'GET';
        xhttp.onload = function() {
            callback(xhttp.responseText);
        };
        xhttp.onerror = function() {
            // Do whatever you want on error. Don't forget to invoke the
            // callback to clean up the communication port.
            callback('Error');
        };
        xhttp.open(method, request.url, true);
        if (method == 'POST') {
            xhttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        }
        xhttp.send(request.data);
        return true; // prevents the callback from being called too early on return
    }
});

The issue I am facing is I keep getting the error Invalid arguments to connect. for chrome.runtime.sendMessage function.

I am not sure what I am missing. Any help us is greatly appreciated.

Answer 1

You have been trying to inject your content script into the page with a <script> tag.

When you do it, your script ceases to be a content script: it executes in the context of the page, and loses all elevated access to Chrome API, including sendMessage.

You should read up on isolated world concept and this question about page-level scripts.

To use jQuery, you should not rely on the copy provided by the page - it's in another context and therefore unusable. You need to include a local copy of jQuery with your files and load it before your script:

1. If you're using the manifest to inject scripts, you can add jQuery to the list before your script:

   "content_scripts": [
     {
       matches: ["http://*.example.com/*"],
       js: ["jquery.js", "content.js"]
     }
   ],
   

2. If you are using programmatic injection, chain-load your scripts to ensure the load order:

   chrome.tabs.executeScript(tabId, {file: "jquery.js"}, function() {
     chrome.tabs.executeScript(tabId, {file: "content.js"});
   });