How to access a particular tab from the Google chrome extension?

Question

JavaScript

Good day.
I'm starting to figure out how to create an extension for chrome and I can't understand the following things:
1. How can I access the location parameter of the browser page itself from the extension itself?
2. How to catch the moment of loading the site itself?
3. How to display a message when the site is loaded? (i.e. a person comes to the ya.ru site, and a message pops up saying that "And there is everything on Yandex" or "Greetings to you, great applicant")
4. What scripts do you need connect to manifest.json and how to do it correctly so that the extension works when the browser starts?
At the moment there is this:
manifest.json:

{
  "manifest_version": 2,
  "name": "Test",
  "version": "1.0",

  "icons": {
    "128": "128.png"
  },

  "background": {
    "scripts": ["background.js","jquery.js"]
  },
  "permissions": [
    "cookies",
    "tabs"
  ],

  "browser_action": {
    "default_title": "Test",
    "default_icon": "128.png",
    "default_popup": "popup.html"
  }

}

background.js

$(document).ready(function () {
    jsonUpload();
});



function jsonUpload() {
    if (localStorage['date_json'] == undefined) {
        localStorage['date_json'] = new Date().getTime();
    }
    if (localStorage['json'] == undefined) {
        jsonLoad()
    }
    tempDate = new Date().getTime();
    var delta = tempDate - localStorage['date_json'];
    if (delta > 3600000) {
        localStorage['date_json'] = new Date().getTime();
        jsonLoad()
    }
    setTimeout(jsonUpload, 10000);
}

function jsonLoad() {
    $.getJSON("/*тут какая нибудь API*/",function(data){
        localStorage['json'] = data;
    });
}
function checkUrl() {
    var array=JSON.parse(localStorage['json']);
    array.forEach(function(item, i, data) {
                // if (item['domen']==chrome)
            });
}

I have only been in this area for a day and the code may seem ugly, but you will forgive me :-)

Answer 1

See API chrome.tabs, there are also events that can be "caught", and access to content, do not forget about permissions.