How to detect Reference Errors in Javascript where Undefined doesn't work?

Question

typeof(nonexistingobj)

returns 'undefined' BUT

typeof(nonexistingobj.nonexistentproperty)

does not generate 'undefined' as I was expecting, but something called a Reference Error - how do I detect this?

I'm trying to do sub-property detection on the response from an API. (Specifically, the API returns a sub object called data.paging.next when there's another page of API results to get, but no 'next' sub object if it just returned the last page).

You get a ReferenceError when trying to reference a property on an object that does not exist. So in your case, obj does not exist (so it's undefined). You can detect this by checking "undefined" === typeof(obj) — Sascha Gehlich
– Sascha Gehlich, Commented Jun 23, 2013 at 16:47
typeof is an operator, not a function. You use it like typeof obj.nonexistentproperty. — basilikum
– basilikum, Commented Jun 23, 2013 at 16:48
You can detect a ReferenceError by wrapping your call in a try-catch statement — Sascha Gehlich
– Sascha Gehlich, Commented Jun 23, 2013 at 16:49

Quentin · Accepted Answer · 2013-06-23 16:49:08Z

3

Don't try to access a property of undefined. Test if the variable you are trying to access is defined first.

if (typeof obj !== "undefined") {
    typeof obj.nonexistentproperty;
}

answered Jun 23, 2013 at 16:49

Quentin

949k136 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

metalaureate Over a year ago

Ahhhh, that does it. Thanks.

Wilker Iceri · Accepted Answer · 2013-06-23 16:56:13Z

0

To catch errors you can use try/catch:

try {
     console.log(typeof nonexistingobj.nonexistentproperty);
} catch (error) {
     console.log('Message error: ' + error.message);
}

answered Jun 23, 2013 at 16:56

Wilker Iceri

4872 silver badges6 bronze badges

Collectives™ on Stack Overflow

How to detect Reference Errors in Javascript where Undefined doesn't work?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related