Catching undefined javascript variable

Question

I'm using Ajax/jsonp to access a remote database. As such, the response.error is never returned. I'm trying to catch an instance when the remote server does not return data for whatever reason. I've tried everything I can think of to catch an undefined condition and I can't seem to catch it. I've tried to find the variable with Firebug. I've tried using just about every combination of the following code I can think of and just can't seem to get it to work.

                      if ( typeof(data.flightStatuses[0].operationalTimes.publishedDeparture.dateLocal) === "undefined") {
                        alert("flightstats is undefined");
                    }

Any ideas greatly appreciated!!!!

I also tried:

                      if ( typeof data.flightStatuses === "undefined") {
                        alert("flightstats is undefined");
                    }

Above code won't execute alert either....

FINALLY! This worked...

if ( typeof data.flightStatuses[0] === "undefined")

I don't really know why, but it did. thanks your everyone's help!

What happens if data, flightStatuses, operationalTimes or publishedDeparture are also undefined? — CodingIntrigue
– CodingIntrigue, Commented Sep 10, 2013 at 15:20
fyi, you don't need typeof unless the leftmost variable may be undefined. in any other case checking for === undefined is pretty safe. Additionally, typeof is an operator, not a function so you can omit the () — ThiefMaster
– ThiefMaster, Commented Sep 10, 2013 at 15:22
OK. GREAT answers. I'll try a couple of these approaches and report back! thanks. — hypermiler
– hypermiler, Commented Sep 10, 2013 at 15:54
&#^$% OK. I tried: if ( typeof data.flightStatuses === "undefined") { alert("flightstats is undefined"); Still, it won't execute the alert..... } — hypermiler
– hypermiler, Commented Sep 10, 2013 at 16:01

Paul · Accepted Answer · 2013-09-10 15:20:37Z

2

If data.flightStatuses is undefined, then data.flightStatuses[0] will throw an error. Make you only check if the relevant identifier is undefined:

if(typeof data.flightStatuses === "undefined") {
    alert("flightStatuses is undefined");
} else {
    // Here you know data.flightStatuses exists, so you can test data.flightStatuses[0]
    if(typeof data.flightStatuses[0] === 'undefined'){
        alert("flightStatuses[0] is undefined");
    } else {
        // And so on, depending on how much you know about your data source
    }
}

answered Sep 10, 2013 at 15:20

Paul

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Comments

jbiz · Accepted Answer · 2019-07-10 00:24:09Z

2

This seems to work

   try {
        dateLocal = typeof (data.flightStatuses[0].operationalTimes.publishedDeparture.dateLocal) !== 'undefined';
        if (dateLocal) {
            // Do something with dateLocal
            // ...
        }
    }
    catch (err) {
        alert("flightstats is undefined: " + err);
    }

edited Jul 10, 2019 at 0:24

answered Sep 10, 2013 at 15:25

jbiz

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1 Comment

gsziszi Over a year ago

"? true : false" not needed

Ronnie · Accepted Answer · 2013-09-10 15:21:53Z

0

Could this work?

if (data.flightStatuses[0].operationalTimes.publishedDeparture.dateLocal) === null) {
                        alert("flightstats is undefined");
                    }

answered Sep 10, 2013 at 15:21

Ronnie

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