getHistoryJs constant

Implementation

static const String getHistoryJs = '''
indexedDB.databases().then((databases) => {
if (databases.length > 0) {
  var bookmarkJson = JSON.stringify([]);
  var dataJson = JSON.stringify([]);
  var lastItemJson = JSON.stringify([]);

  var blobToBase64 = function(blob) {
    return new Promise(resolve => {
      let reader = new FileReader();
      reader.onload = function() {
        let dataUrl = reader.result;
        resolve(dataUrl);
      };
      reader.readAsDataURL(blob);
    });
  }

  function getAllFromIDBStore(storeName) {
    return new Promise(
      function(resolve, reject) {
        var dbRequest = indexedDB.open("books");

        dbRequest.onerror = function(event) {
          reject(Error("Error opening DB"));
        };

        dbRequest.onupgradeneeded = function(event) {
          reject(Error('Not found'));
        };

        dbRequest.onsuccess = function(event) {
          var database = event.target.result;

          try {
            var transaction = database.transaction([storeName], 'readwrite');
            var objectStore;
            try {
              objectStore = transaction.objectStore(storeName);
            } catch (e) {
              reject(Error('Error getting objects'));
            }

            var objectRequest = objectStore.getAll();

            objectRequest.onerror = function(event) {
              reject(Error('Error getting objects'));
            };

            objectRequest.onsuccess = function(event) {
              if (objectRequest.result) resolve(objectRequest.result);
              else reject(Error('Objects not found'));
            };
          } catch (e) {
            console.log(JSON.stringify({messageType: "error", error: e.name}));
            reject(Error('Error getting objects'));
          }
        };
      }
    );
  }

  async function getTtuData() {
    try {
      items = await getAllFromIDBStore("data");
      await Promise.all(items.map(async (item) => {
        try {
          item["coverImage"] = await blobToBase64(item["coverImage"]);
        } catch (e) {}
      }));

      dataJson = JSON.stringify(items);
    } catch (e) {
      dataJson = JSON.stringify([]);
    }

    try {
      bookmarkJson = JSON.stringify(await getAllFromIDBStore("bookmark"));
    } catch (e) {
      bookmarkJson = JSON.stringify([]);
    }

    try {
      lastItemJson = JSON.stringify(await getAllFromIDBStore("lastItem"));
    } catch (e) {
      lastItemJson = JSON.stringify([]);
    }

    console.log(JSON.stringify({messageType: "history", lastItem: lastItemJson, bookmark: bookmarkJson, data: dataJson}));
  }

  try {
    getTtuData();
  } catch (e) {
    console.log(JSON.stringify({messageType: "history", lastItem: lastItemJson, bookmark: bookmarkJson, data: dataJson}));
  }
} else {

  console.log(JSON.stringify({messageType: "empty"}));

}
});
''';