popup.js

let startDatePicker = document.getElementById("startDate");
let endDatePicker = document.getElementById("endDate");
let today = new Date();
const dtf = new Intl.DateTimeFormat('en', {year:"numeric",month:"2-digit",day:"2-digit"});
[{ value: mo },,{ value: da },,{ value: ye }] = dtf.formatToParts(today);
endDatePicker.value=`${ye}-${mo}-${da}`;

chrome.storage.sync.get(['year','month','day'], function(result) {
    previousDate = new Date(result['year'], result['month'], result['day']);
    [{ value: mo },,{ value: da },,{ value: ye }] = dtf.formatToParts(previousDate);
    startDatePicker.value=`${ye}-${mo}-${da}`;
});

chrome.storage.sync.get({link: ''}, function(result) {
    if( result['link'] ) {
        var addDiv = document.getElementById("adress");
        var button = document.createElement("input");
        button.type = "button";
        button.value = "Copy link";
        button.addEventListener('click', function() {
            navigator.clipboard.writeText(result['link']).then(
                function() {
                    chrome.browserAction.setBadgeText({text:""});
                    chrome.storage.sync.set({'link': ''});
                    window.close();
                }
            );
        });
        addDiv.appendChild(button);
    }
});

let getAdress = document.getElementById("getAdress");
getAdress.addEventListener("click", async () => {
    let startDate = startDatePicker.valueAsDate;
    let endDate = endDatePicker.valueAsDate;
    let newDate = new Date(new Date().setDate(endDate.getDate()+1));

    chrome.storage.sync.set({'year': newDate.getFullYear(),
                             'month': newDate.getMonth(),
                             'day': newDate.getDate(),
                             'startYear': startDate.getFullYear(),
                             'startMonth': startDate.getMonth(),
                             'startDay': startDate.getDate(),
                             'endYear': endDate.getFullYear(),
                             'endMonth': endDate.getMonth(),
                             'endDay': endDate.getDate()},
                            function() {
                                chrome.tabs.create(
                                    {url: "https://runkeeper.com/exportData", active: false},
                                    function (tab) {
                                        chrome.runtime.sendMessage({action: "tabCreated"});
                                    }
                                );
                            });
    window.close();
});