Promise not resolving and not returning expected value:

Question

I'm trying to adapt IndexedDB to a promise, but the function checkUrlLink doesn't return any value. How can I fix this promise?

This is my code:

var promise = new Promise(function(resolve) {
        return checkUrlLink(send_to_url, event);
    }).then(function(url_link) {
        console.log('URL LINK in promisse' + url_link);
        return clients.openWindow(url_link);
    });


function checkUrlLink(send_to_url, event) {

  return new Promise((resolve,reject) =>  {

    var request = indexedDB.open('db', 1);
    var original_event = event;

    request.onsuccess = function (event) {
      //db = event.target.result;
      var url_link = "url_link";
      var store = request.result.transaction("uid", "readwrite").objectStore("uid");
      var getRequest = store.get(url_link);

      getRequest.onsuccess = function () {
        var result = getRequest.result;
        if (result) {
          url_link = result;
          //send_to_url(original_event,url_link);
          resolve(url_link);
        } else {
          url_link_value = self.registration.scope;
          store.add(url_link_value, url_link);
          //send_to_url(original_event, url_link_value);
          resolve(url_link_value);
        }
      };
    };

    request.onupgradeneeded = function (event) {
      var db = event.target.result;
      var store = db.createObjectStore('url_link');
    };



  });



}

I'm executing this inside a service worker.

Answer 1

You are using a Promise constructor anti-pattern here

var promise = new Promise(function(resolve) {
    return checkUrlLink(send_to_url, event);
}).then(function(url_link) {
    console.log('URL LINK in promisse' + url_link);
    return clients.openWindow(url_link);
});

ie you're wrapping a function that returns a promise inside a new Promise - there's no need for that. However, you never call resolve either, so that's two problems with that code

The above code is simply

var promise = checkUrlLink(send_to_url, event)
.then(function(url_link) { 
    console.log('URL LINK in promisse' + url_link); 
    return clients.openWindow(url_link); 
};

now promise is a promise that will resolve to the value returned by clients.openWindow(url_link);