how to check for an attribute that can be undefined or have a value in Javascript/Jquery?

Question

I need to check for an attribute inside the Jquery Mobile transition data object. The attribute can either be undefined or has a value of dialog or some other value.

Originally I only checked like this:

$(document).on( "pagebeforechange", function( e, data ) {
    if(  A && B && data.options.role != "dialog" ){
        // do something
        }
     });

However, this way I never enter the if-clause when data.options.role is undefined. I'm currently trying like this but am not really getting anywhere:

$(document).on( "pagebeforechange", function( e, data ) {
    if(  A && B && data.options.role != "undefined" && data.options.role != "dialog" ){
        // do something
        }
     });

Question
How can I make sure the value is queries and passes into the IF clause if it's either undefined or has a value, which is not dialog?

Thanks for help!

id data.options.role is undefined, then your first if statement should be hit. What are A and B looking for? — Rory McCrossan
– Rory McCrossan, Commented May 29, 2012 at 10:41
data.options.fromHashChange == true and self.options._transDelta == 1 - both are ok and working correclty. Only after adding the third check for dialog, I'm not getting into the IF if "undefined" — frequent
– frequent, Commented May 29, 2012 at 10:44
possible duplicate of Detecting an undefined object property in JavaScript and How to check for undefined in javascript?. — Felix Kling
– Felix Kling, Commented May 29, 2012 at 10:46
Are you sure A and B are true? You can see from the following fiddle that your original condition is hit when .role is undefined: jsfiddle.net/RoryMcCrossan/NSDgL/1 — Rory McCrossan
– Rory McCrossan, Commented May 29, 2012 at 10:48
hm. seems to be another error... need more than 1sec. Thanks for the pointer! — frequent
– frequent, Commented May 29, 2012 at 10:58

Sarfraz · Accepted Answer · 2012-05-29 10:42:15Z

1

If you meant undefined type of javascript, for that you need to use typeof like this:

if(  A && B && typeof data.options.role != "undefined" &&
      data.options.role != "dialog" )

You also need to make sure that A and B are coming truthy too.

answered May 29, 2012 at 10:42

Sarfraz

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