Return value for function that there is a callback function inside

Question

I write a function to check does an item exist in list that was stored in storage. Everything is ok, just problem to return value for function. Here is my code:

function isExistInWhitelist(s){
    var res = false;
    chrome.storage.local.get("whitelist", function(result){
        for(var i = 0; i< result.whitelist.length; i++)
            if(result.whitelist[i].indexOf(s)>=0){
                res = true;//[1]
                break;
            };
    });
    return res;
}

When I use console.log to write res value in [1], result is ok (true), but I cannot return value for isExistInWhitelist function. What need I do?