Chrome storage giving undefined for stored timer

Question

I am making a chrome extension, and I am using chrome storage to store a variable. Actually I am first inputing a timer from user, and then refreshing the page after every T seconds those are given as input by user. So to store this time I used chrome storage like this :

chrome.extension.onMessage.addListener(function(request, sender, sendResponse) {
var currentTimer = request.timer;
if(currentTimer!=null){
    currentTimer = currentTimer*1000;
    alert(currentTimer);
    chrome.storage.sync.set({'x': currentTimer}, function() {
            console.log(currentTimer);
    });
}
if(currentTimer==null){
    chrome.storage.sync.get('x', function(items){
           currentTimer = items.value;
    });
    //Here currentTimer is undefined.
}
});

Can anyone help why currentTimer is still undefined. I am debugging for very long time, but could not arrive at a solution.

The problem is that as soon as page is refreshed currentTimer will get NULL value as it is been entered only once by user.

@wOxxOm Can you please elaborate a solution for it then ?What you mean by you can't immediately return the value. You should send it back in a new message to your content script from the sync.get callback. ? — GitCoder, Sep 20 '15 at 14:54
Look at [that question](http://stackoverflow.com/q/14220321/3959875). Seems the best duplicate candidate and provides some good explanations of the problem. — wOxxOm, Sep 20 '15 at 15:12
possible duplicate of [Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference](http://stackoverflow.com/questions/23667086/why-is-my-variable-unaltered-after-i-modify-it-inside-of-a-function-asynchron) — Teepeemm, Sep 20 '15 at 20:25

score 1 · Answer 1 · answered Sep 20 '15 at 15:08

All chrome.* API callbacks are invoked asynchronously when the originating function has already finished, which also means that the next statement after chrome.* API call is executed before the callback.

Put the code that needs the result into the callback:

chrome.storage.sync.get('something', function(item) {
       setTimeout(someFunction, item.value);
});

In case the result is needed in a content script, return the value in a new message:

content script:

chrome.runtime.sendMessage({request: "doSomething"});

chrome.runtime.onMessage.addListener(function(msg) {
    if (msg.response) {
        // do something with the received msg.response
    }
});

background script:

chrome.runtime.onMessage.addListener(function(msg, sender, sendResponse) {
    if (msg.request == "doSomething") {
        var tabId = sender.tab.id, frameId = sender.frameId;
        chrome.storage.sync.get('something', function(item) {
            sendMessageToFrameId(tabId, frameId, {response: item.value});
        });
    }
});

function sendMessageToFrameId(tabId, frameId, msg) {
    // 1. frameId works since Chrome 41 and throws on prior versions
    // 2. without frameId Chrome 45 sends the message to wrong tabs
    try { chrome.tabs.sendMessage(tabId, msg, {frameId: frameId}); }
    catch(e) { chrome.tabs.sendMessage(tabId, msg); }
}

Chrome storage giving undefined for stored timer

1 Answers1