sendMessage from background script to content script in app fails

Question

UPDATE

From what I can tell, it is impossible to send a message from the background script to the content script using the "sendMessage" function. However there is a horrible workaround,

In your content script's window.onload, send a message to the background script:

chrome.runtime.sendMessage( { action: "messaging", window: "app" }, this.listenForFutureMessages );

Also in the content script, have the following function:

listenForFutureMessages: function(someAction)
{
    //Take some action based on the message

    //If we want the background script to be able to contact
    //us again, we need to give them another callback. This
    //is because Chrome only allows one use per callback
    chrome.runtime.sendMessage( { action: "messaging", window: "app" }, this.listenForFutureMessages );
},

In the background script, have a listener that does something like this:

chrome.runtime.onMessage.addListener(
    function(request, sender, sendResponse)
    {
        if ( request.action === "messaging" )
        {
            //Save the callback for later
            this.listeners[ request.window ] = sendResponse;

            //Tell chrome we will be using the callback later
            return true;
        }
    }
);

When your background script wants to send the content script a message, simply call it like this:

this.listeners[ "app" ]( { someProperty: "some value" } );

This is a stupid way to do this, but it makes this actually possible. Hope this helps anyone else who needs this functionality.

ORIGINAL I'm unable to send a message from my background script to a content script. When I try to find the tab id, it tells me I don't have permissions even though my app has that permission. And when I receive a message from the content script, and print out the sender object, it shows tab.id = -1. The API to send a message to a content script requires a tab id!

chrome.tabs.sendMessage(integer tabId, any message, function responseCallback)

The error:

chrome.tabs is not available: You do not have permission to access this API. Ensure that the required permission or manifest property is included in your manifest.json.

Error in event handler for 'undefined': Cannot call method 'sendMessage' of undefined TypeError: Cannot call method 'sendMessage' of undefined at chrome-extension://panoaieakcofaegcjfbmhndaekfgpijh/scripts/background.js:109:16 at Event.dispatchToListener (event_bindings:356:21) at Event.dispatch_ (event_bindings:342:27) at Event.dispatch (event_bindings:362:17) at miscellaneous_bindings:167:33 at Event.dispatchToListener (event_bindings:356:21) at Event.dispatch_ (event_bindings:342:27) at Event.dispatch (event_bindings:362:17) at Object.chromeHidden.Port.dispatchOnMessage (miscellaneous_bindings:253:22)

So how do I contact my content script? (I have multiple windows and need to be able to contact them individually)

My manifest:

{
    "manifest_version": 2,
    "name": "App",
    "description": "App",
    "version": "0.75",
    "minimum_chrome_version": "27",
    "offline_enabled": true,
    "icons": 
    {
        "16": "images/icon16.png",
        "48": "images/icon48.png",
        "128": "images/icon128.png"
    },
    "app": 
    {
        "background": 
        {
            "scripts": 
            [
                "scripts/background.js"
            ]
        }
    },
    "permissions": 
    [
        "unlimitedStorage",
        "fullscreen",
                {
            "fileSystem": 
            [
                "write"
            ]
        },
        "background",
        "<all_urls>",
        "tabs"
    ],
    "update_url": "http://192.168.1.121/app.xml"
}

Don't put your answer inside the question. If you have an answer, post it as answer. — avpaderno
– avpaderno, Commented Jul 1, 2013 at 0:19
@kiamlaluno I don't consider it an answer. It's a workaround. — Don Rhummy
– Don Rhummy, Commented Dec 11, 2013 at 20:05

Rob W · Accepted Answer · 2013-06-29 21:08:28Z

1

There's not such a thing called "Content scripts" in a Chrome app. Your manifest file looks like a mixture of a Chrome extension. Open chrome://extensions/, enable developer mode, and you would see a warning that the "background" and "tabs" permissions are invalid for a Chrome app.

If you're implementing a Chrome app, just use chrome.runtime.sendMessage and chrome.runtime.onMessage. These messages can be send from and to your event page and the main page. For example:

// event page (aka background page)
chrome.app.runtime.onLaunched.addListener(function() { 
    chrome.app.window.create('main.html');
});

    // Later, when you want to notify the app window
    chrome.runtime.sendMessage(" ... any message ... ");

<!-- main.html -->
<script src="main.js"></script>

// main.js
chrome.runtime.onMessage.addListener(function(message, sender, sendResponse) {
    // Do something with the message
});

answered Jun 29, 2013 at 21:08

Rob W

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4 Comments

Don Rhummy Over a year ago

This does not work for me (it's exactly what I tried to do). The main.js never receives the message. I may have used the wrong terminology but my"main page" never receives that message.

Rob W Over a year ago

@DonRhummy Then show your real manifest and code instead of something else that doesn't seem to represent your code.

Don Rhummy Over a year ago

That is my manifest. You'll notice it does not declare any content scripts. Even removign the background and tabs permissions does not make this work.

Rob W Over a year ago

@DonRhummy Please provide your source code in your question. Otherwise, I can only guess what's wrong with your code (my attempt to reproduce your environment failed, so it's up to you to provide a self-contained example which demonstrates your issue).

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