Tampermonkey / Greasemonkey Dexie.js database storage in javascript

TestDatabase.user.js

// ==UserScript==
// @name         TESTDatabase
// @namespace    foobar.com
// @version      0.1.1
// @description  testing database functionality
// @include      https://sample.somesite.com/*
// @require      https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js
// @require      https://unpkg.com/dexie@latest/dist/dexie.js
// @grant        GM_getValue
// @grant        GM_setValue
// @grant        GM.getValue
// @grant        GM.setValue
// ==/UserScript==
/* global $ */
/* eslint-disable no-multi-spaces, curly */

(function () {
    'use strict';

    const MAX_VALUE_INT = 2147483647;
    const dbName = 'proof-of-concept-db-test-6';
    const tmObj = 'proof-concept-tm-obj-6';

    // database ref for use right when the TamperMonkey script loads on the current page
    var db = initDB();

    function initDB() {
        console.log('initDB - start');

        // #1 check to see if Tampermonkey already has the database stored;
        let tmDBObj = GM.getValue(tmObj);
        tmDBObj.then(
            function (data) {
                if (data == null) {
                    console.log('tampermonkey does not hold the database');
                    let databaseTEST = new Dexie(dbName);
                    databaseTEST.version(1).stores(
                        { logHistory: '++id,state,elapsedtime' }
                    );
                    // I think dexie require opening the database at least once, thus doing it when creating the database
                    let openData = databaseTEST.open();
                    openData.then(
                        function (data) {
                            console.log('opened the database! - ' + data);
                            return databaseTEST.logHistory.add(
                                {
                                    state: 'Sample-State',
                                    time: new Date().getTime()
                                }
                            );
                        }
                    ).catch(
                        function (e) {
                            console.log('error --- ' + e);
                        }
                    );
                    GM.setValue(tmObj, JSON.stringify(databaseTEST));
                } else {
                    console.log('tampermonkey has a stored database, time to load it up!');
                    let openDBFromFile = JSON.parse(GM.getValue(tmObj)); // this should be our Dexie DB
                    let results = openDBFromFile.logHistory
                        .where("id")
                        .between(0, MAX_VALUE_INT); // line throws error, "SyntaxError: JSON.parse: unexpected character at line 1 column 2 of the JSON data"
                }
            }
        ).catch(
            function (error) {
                console.log('error - ' + error);
            }
        );
    }
})();

Posted on behalf of the Stackoverflow question - https://stackoverflow.com/q/57929417/6393165

Intended use - store a database in a Tampermonkey storage in order to access cross sites.