undefined, how you work?

Question

Just a simple question :)

if I have :

var user = {'name': 'Fred'};

So

console.log(user.name); // Fred
console.log(user.age); // undefined

But

console.log(test); // ReferenceError: test is not defined

I don't understand why because for me it's the same as

console.log(window.test); // undefined

In my project, i try to check if a global variable exist but I have a referenceError... I don't really understand why the followinf code doesn't work...

if (TestGlobal) // ReferenceError: TestGlobal is not defined
   console.log(' allo 1 ');

if (typeof(TestGlobal ) !== 'undefined') // Ok
   console.log(' allo 1 ');

Note that referencing a variable `test` as a property of `window` will work _only_ if `test` is a global variable. — nnnnnn, Feb 07 '13 at 11:12
Take a look here: http://stackoverflow.com/questions/10102862/referenceerror-and-the-global-object — Mickael, Feb 07 '13 at 11:13

score 1 · Accepted Answer · answered Feb 07 '13 at 11:45

…and a simple answer:

Property references always evaluate to their value or the undefined value if the key does not exist, as long as the base value is not undefined (then a TypeError would be thrown).
Variables throw ReferenceErrors if not defined before, unless they are used with the typeof keyword (where they just evaluate to "undefined").

undefined, how you work?

1 Answers1