Wait for Function to complete and then return a va

Question

I have this function Offline.check(); , which takes 1 seconds to execute..So below function is not waiting for it and it always return false on first time.I used set time out..but thats always returning null.

  function checkstats()

    {

    Offline.check(); // This returns Offline.state=up  or down and it takes 1 seconds to complete.

    if(Offline.state=="up")
    {
    return true;
    }

    else
    {
    return false;
    }

    }

var a = checkstats();

Answer 1

You can use Asynchronous JavaScript to address the issue. There are several ways of implementing asynchronous behaviour in JavaScript. You can use Callbacks, Listeners or Promises.

Anyway, if you are certain that it only takes 1 second, setTimeout in a callback function and allow Offline.check() to complete. (If it's external or lazy to implement async there)

doOfflineCheck(function(){
    if(Offline.state=="up")
    {
    return true;
    }
    else
    {
    return false;
    }
});

function doOfflineCheck(cb){
    setTimeout(function(){
    Offline.check();
    },1000);
}

Answer 2

Ideally you could set a callback function with Offline.check, but I understand it is external, so that won't work.

You can use a timeout to wait for Offline.state to get set, but then you'll need to do any actions involving the variable a asynchronously too:

function checkstats(callBack){  // checkstats() now takes a callback
    Offline.check();  // Start Offline.check() as usual

    setTimeout(function(){  // Set a timeout for 1 second
        if(Offline.state=="up")  // After 1 second, check Offline.state as usual
        {
            callBack(true);  // ...but we call the callback instead of returning
        }
        else
        {
            callBack(false);  // ...but we call the callback instead of returning
        }
    }, 1000);
}

checkstats(function(a){ // This anonymous function is the callback we're using
    // Now you can use "a" normally
});

If you're not sure that Offline.check() will take exactly 1 second, you can use an interval instead of a timeout, and try every second for, say, 5 seconds:

function checkstats(callBack){
    Offline.check();

    var attempt = 0, maxAttempts = 5;
    var checkStatsInterval = setInterval(function(){
        if(++attempt > maxAttempts){
            // Ran out of attempts, just give up
            clearInterval(checkStatsInterval);
            alert('Waited '+maxAttempts+' seconds for Offline data. Giving up!');
            return;
        }
        if(Offline.state){
            clearInterval(checkStatsInterval);

            // It's loaded! Now confidently check Offline.state
            if(Offline.state=="up")
            {
                callBack(true);
            }
            else
            {
                callBack(false);
            }
        }
    }, 1000);
}

checkstats(function(a){
    // Now you can use "a" normally
});