background.js

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

'use strict';

chrome.runtime.onInstalled.addListener(function() {
    console.log("hello world.");
    
    chrome.storage.sync.set({color: '#3aa757'}, function() {
       console.log("The color is green.");
    });

    chrome.declarativeContent.onPageChanged.removeRules(undefined, function() {
        chrome.declarativeContent.onPageChanged.addRules([{
            conditions: [new chrome.declarativeContent.PageStateMatcher({
                pageUrl: { hostEquals: 'developer.chrome.com' },
            })
            ],
            actions: [new chrome.declarativeContent.ShowPageAction()]
        }]);
    });

});