indexedDB reusable function

Question

I'm making some prototype app who is using indexdDB and I can't figure out how to create reusable function. For example I would like to create reusable function to retrieve LOV values. I know that it should be create somehow via events but I can't figure out how. Could anyone please help?

Below is the code what I would like to bring in life

function parent(){
    var lovValues = getLovValuesByType("STORE_TYPE");
    //lovType now is undefined
};

function getLovValuesByType(lovType){
    var returnedLovValues = new Array();
    var t = db.transaction(["LST_OF_VAL"], "readonly");
    var objectStore = t.objectStore("LST_OF_VAL");
    var INDEX = objectStore.index("TYPE");
    var REQUEST = INDEX.openCursor(IDBKeyRange.only(lovType));
    REQUEST.onsuccess = function() {
        var CURSOR = REQUEST.result;
        if (CURSOR) {
            var value = this.result.value.VAL;
            returnedLovValues.push(value);
            this.result.continue();
        } else {
            return returnedLovValues; /// <------return data
        };
    };
};

Answer 1

Your return statement is returning from the callback function REQUEST.onsuccess. You don't return anything from getLovValuesByType, which is why lovValues is undefined.

The most straightforward solution is to use a callback function:

getLovValuesByType("STORE_TYPE", function (lovValues) {
    //lovType now is defined
);

function getLovValuesByType(lovTypem, cb){
    var returnedLovValues = new Array();
    var t = db.transaction(["LST_OF_VAL"], "readonly");
    var objectStore = t.objectStore("LST_OF_VAL");
    var INDEX = objectStore.index("TYPE");
    var REQUEST = INDEX.openCursor(IDBKeyRange.only(lovType));
    REQUEST.onsuccess = function() {
        var CURSOR = REQUEST.result;
        if (CURSOR) {
            var value = this.result.value.VAL;
            returnedLovValues.push(value);
            this.result.continue();
        } else {
            cb(returnedLovValues);
        };
    };
};

More generally, you might want to do some reading about asynchronous JavaScript.