Check whether user has a Chrome extension installed

Question

I am in the process of building a Chrome extension, and for the whole thing to work the way I would like it to, I need an external JavaScript script to be able to detect if

Answer 1

Webpage interacts with extension through background script.

manifest.json:

"background": {
    "scripts": ["background.js"],
    "persistent": true
},
"externally_connectable": {
    "matches": ["*://(domain.ext)/*"]
},

background.js:
chrome.runtime.onMessageExternal.addListener(function(msg, sender, sendResponse) {
    if ((msg.action == "id") && (msg.value == id))
    {
        sendResponse({id : id});
    }
});

page.html: