MyApphow to check for "typeof MyApp.User.current.language"

Question

Possible Duplicate:
javascript test for existence of nested object key

if (typeof MyApp != 'undefined' &&
    typeof MyApp.User != 'undefined' &&
    typeof MyApp.User.current != 'undefined' &&
    typeof MyApp.User.current.language != 'undefined') {

   console.log(MyApp.User.current.language);
}

this feels wrong. Can this if statement be written in some nicer way?

Where did that `Siag` come from? – Richard JP Le Guen Oct 12 '11 at 15:32 — Richard JP Le Guen, Oct 12 '11 at 15:32
thanks richard. fixed. was a c&p bug. – Simon Oct 12 '11 at 15:46 — Simon, Oct 12 '11 at 15:46

jfriend00 · Answer 1 · 2011-10-12T15:51:35.110

One simple way is this:

try {
    console.log(MyApp.User.current.language);
} catch(e) {}

or if you don't want "undefined" to be output if MyApp.User.current exists, but MyApp.User.current.language does not, then you would use this:

try {
    if (typeof MyApp.User.current.language != 'undefined') {
        console.log(MyApp.User.current.language);
    }
} catch(e) {}

The try/catch catches the cases for when MyApp or MyApp.user or MyApp.User.current are not defined so you don't have to test for them individually.

score 1 · Answer 2 · answered Oct 12 '11 at 15:39

You could perform a decompose conditional refactoring and put that condition in a function:

if (currentLanguageIsDefined()) {
   console.log(MyApp.User.current.language);
}

function currentLanguageIsDefined() {
    return typeof MyApp != 'undefined' &&
           typeof MyApp.User != 'undefined' &&
           typeof MyApp.User.current != 'undefined' &&
           typeof MyApp.User.current.language != 'undefined';
}

... or you can take advantage of the fact that the && operator returns the last value evaluated:

var lang;
if(lang = getCurrentLang()) {
    console.log(lang);
}

function getCurrentLang() {
    return MyApp && MyApp.User && MyApp.User.current && MyApp.User.current.language;
}

MyApphow to check for "typeof MyApp.User.current.language"

2 Answers2