I'm trying to reference information from my background.html page (that is accessing localStorage) by sending a request from my content script using the messaging API. I am able to successfully send and receive a response, but what I am able to do with the response is throwing me for a loop.

This works:

Code:

function getStoredPrefs()
{
	chrome.extension.sendRequest({name: "getPreferences"}, function(response) { console.log(response.prefEnableKey) ;} );
}

This doesn't work:

Code:

function getStoredPrefs()
{
	var responseVal = "";
	chrome.extension.sendRequest({name: "getPreferences"}, function(response) { responseVal = response.prefEnableKey ;} );
	alert(responseVal);
}

Side note: When I call the alert in the portion that is not working, it seems to fire twice (two separate alert boxes received) even though I am only calling it once. Any ideas?

Thanks in advance for any assistance.

First up, why did you feel the need to make a new account to post the same question?....
Console.log returns value, alert of same response is blank???
...if its because no one answered your question then Im sorry coz Ive been busy the last few days and havent touched the computer other than to answer emails and play Torchlight.

The reason your alert is not getting the variable is because its being exectuted before the variable arrives.....

Code:

chrome.extension.sendRequest({name: "getPreferences"}, function(response) { responseVal = response.prefEnableKey ;} );

...in your sendRequest your stating that your "callback" is the anonymous function....

Code:

function(response) { responseVal = response.prefEnableKey ;}

this gets called after the request has been got, when this is can be anytime so the alert will prolly happen before the response is got.

Another way to write your code that may help you see it is....

Code:

function prefsResponse(response)
{
    responseVal = response.prefEnableKey ;
}

function getStoredPrefs()
{
	var responseVal = "";
	chrome.extension.sendRequest({name: "getPreferences"}, prefsResponse()  );
	alert(responseVal);
}

(hope i got that right, i didnt test it and Im prone to silly mistakes...can never remember details)
If you where to put your alert in prefsResponse you would see that it gets the value.
Callbacks are annoying but something you've got to work with alot in chrome extensions.

Also, you dont need to message to get stuff from localstorage (I guess thats what your doing), Im not sure whats its scope is exactly but anyways you can get it from the background page doing something like this....

Code:

var backgroundPage = chrome.extension.getBackgroundPage();
value=backgoundPage.localstorage.prefEnableKey;

Asfar as the double alert I saw something on google groups about this recently and apparently it was a bug that got fixed in one of the latest dev updates (cant remember the thread).

Hope this helps, Im not allways the best at explaining stuff.

PAEz, it would be:

Code:

chrome.extension.sendRequest({name: "getPreferences"}, prefsResponse );

Because the intention is to pass the function by reference, and not to execute the function and pass the return value.
Also it's localStorage, with a capital S.

Also callbacks aren't that tough, you just have to work with them. Really, JavaScript makes them a lot easier than other languages:

Code:

function getStoredPrefs(){
	var responseVal = "";
	chrome.extension.sendRequest({name: "getPreferences"}, function(response) {
		responseVal = response.prefEnableKey ;
		alert(responseVal);
	});
}

This (putting the alert in the callback) is what you should be doing, in my personal formatting style.

Remember, JavaScript isn't going to hang to wait for the callback to be run, it doesn't even know you passed a callback. So sequentially all you're doing is chrome.extension.sendRequest() then alert() - no anonymous function till the Background Page gets around to it.

All, thanks for your assistance!

So I updated to the following and the alert is producing the correct results:

Code:

function getStoredPrefs(){
	var responseVal = "";
	chrome.extension.sendRequest({name: "getPreferences"}, function(response) {
		responseVal = response.prefEnableKey ;
		alert(responseVal);
	});
}

My next question: How do I reference the value of responseVal outside of this function within the rest of my code?

Code:

getStoredPrefs();
if(responseVal == "no")
{
	alert("Not toggling");
}
else
{
	alert("Toggling");
}

Console log shows that responseVal is undefined. I know I'm running into issues with the private declaration of responseVal inside my getStoredPrefs function.

Thanks again for the assistance (and sorry about the double post of the same question, I have originally used a bugmenot account but wasn't sure I'd get a response on that account, so I created my own since I'll be frequenting this forum).