IndexedDB retrieving records with a promise

Question

I am storing records in an IndexedDB. I need to write a function to get records and return them to in JSON format to a data grid. The values are also in JSON.

This code doesn't really work because of the asynchronous nature of the IndexedDB calls.

How can I rework this to better use of maybe a promise to get the data?

function getRecords(skip, take) {
    var transaction = db.transaction("docs", "readonly");
    var objectStore = transaction.objectStore("docs");
    var result = "";
    var request = objectStore.openCursor(IDBKeyRange.bound(skip,skip+take))
        .onsuccess = function(evt) {  
            var cursor = evt.target.result;  
            if (cursor) {  
                result = JSON.stringify(cursor.value) + ',';
                cursor.continue();
            }
            return result.substr(0, result.length-1);
        };
}

Called like this:

var recordData = '[' + getRecords(1,10) + ']';

Adding full code

Jeremy J Starcher · Accepted Answer

To promisify this code would be something like:

EDIT: Fixed stupid syntax error

function getRecordsAsync(skip, take) {
    return new Promise((resolve, reject) => {
        var transaction = db.transaction("docs", "readonly");
        var objectStore = transaction.objectStore("docs");
        var result = "";
        var request = objectStore.openCursor(IDBKeyRange.bound(skip, skip + take))
            .onsuccess = function(evt) {
                var cursor = evt.target.result;
                if (cursor) {
                    result = JSON.stringify(cursor.value) + ',';
                    cursor.continue();
                }
                resolve(result.substr(0, result.length - 1));
            }
            .onerror = function(err) {
                reject(err);
            };
    });
}


getRecordsAsync(1, 10).then(data => {
console.log(data);

EDIT

OK, I tracked down the error you were getting -- it was an uncaught rejection in the promise. I should have seen that myself.

This code catches the error properly.

I've tried to track down what the error is, but I wasn't getting anything useful out of the system and I don't know indexeddb at all.

            $("#btnPrint").click(function () {                
                window.finished = false;
                var output = $("#printOutput");
                getRecordsAsync(1,10).then( data => {
                    output.html(data);
                }).catch(err => {
                  console.log("There was an error calling getRecordsAsync");
                  console.log(event);
                });
            });

IndexedDB retrieving records with a promise

Answers (1)

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