Listening any event triggered to window(using window.post()) from an script in manifest v3

[Sudha Kumari]

Hi Folks,

I have an web application which trigger an event "captueScreenshot" to window using window.post() function.

My chrome extension(manifest v2) listen this event 
Using

window.addEventListener("message", (event) => {

    if (event.source !== window)

        return;

    if (event.data.type && (event.data.type === "CaptureScreenshot")) { // does something } }) I am working on migration of manifest v2 to manifest v3, and above code doesn't work in this scenario How can I resolve this?

[Deco]

You are using a background page, this has been replaced with service workers for Manifest V3 which is why it will not work. Replace the code to listen to a content script and when it captures the relevant event, it should send the message to the service worker. Something akin to this:

Content script:

window.addEventListener("message", (event) => {
    if (event.source !== window)
        return;

    if (event.data.type && (event.data.type === "CaptureScreenshot")) {

        chrome.runtime.sendMessage({ action: "captureScreenshot" });
    }
});

 Service worker:
chrome.runtime.onMessage.addListener(
    function(request, sender, sendResponse) {
        if (request.action === "captureScreenshot") {
            // Perform screenshot capture or other actions
        }
    }
);

Thanks,

Deco

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[wOxxOm]

Assuming this is the content script, your old code should work in ManifestV3, so the problem is something else. Debug it in devtools or provide more info to us.

[Sudha Kumari]

Yes,  It is content script.

I am not able to see the content script of my extension injected in the devtool's source.

[wOxxOm]

Assuming you look in the correct place (devtools -> Sources panel -> Content script sub-panel), it means the content script didn't run.

It can happen due to a mistake in its declaration e.g. the wrong "matches".

If you use chrome.scripting to inject/register the script then debug that code as it probably just never runs or there's a mistake in the parameters or your "host_permissions" doesn't match the site. It can be caused by administrative policies that forbid access for extensions: open chrome://policy and see if it has ExtensionSettings with runtime_blocked_hosts inside. Another mistake is to switch the site access in the right-click menu of the extension's icon or in details of the extension in chrome://extensions page.