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

I used the cookie method:

In my manifest.js file I included a content script that only runs on my site:

 "content_scripts": [
        {
        "matches": [
            "*://*.mysite.co/*"
            ],
        "js": ["js/mysite.js"],
        "run_at": "document_idle"
        }
    ], 

in my js/mysite.js I have one line:

document.cookie = "extension_downloaded=True";

and in my index.html page I look for that cookie.

if (document.cookie.indexOf('extension_downloaded') != -1){
    document.getElementById('install-btn').style.display = 'none';
}