How do I determine if variable is 'undefined' or 'null'. My code is as follows:
EmpName = $("div#esd-names div#name").attr('class');
if(EmpName == 'undefined'){
///DO SOMETHING/////
};
views:
503answers:
4
A:
Use typeof:
if (typeof(EmpName) === 'undefined') {
// blah blah blah
}
kevingessner
2010-04-15 18:14:00
You don’t need to put `EmpName` in parentheses; `typeof` is an operator and not a function.
Gumbo
2010-04-15 18:16:12
I know; I just think it reads better this way, and it is valid.
kevingessner
2010-04-15 18:18:46
Putting that operand in parentheses is like doing something like this: `(((1)+(1))===(2))`. It’s absolutely valid but also unnecessary.
Gumbo
2010-04-15 18:21:06
typeof null = 'object' // true
M28
2010-04-15 18:26:16
@Gumbo define unary operator vs unary function.
Evan Carroll
2010-09-24 17:01:18
[answer here](http://stackoverflow.com/questions/3786467/why-typeof-is-called-operator-instead-of-function/3786502#3786502)
Evan Carroll
2010-09-24 17:08:31
@Evan Carroll: An operator is part of the language syntax; a function part of a language library that is defined using the language syntax.
Gumbo
2010-09-24 17:08:39
Is this a general explanation or specific to Javascript? In Haskell (+) is and (-) and part of the standard library. I'm happy with the answer I posted above.. I was just curious I see this point parroted and not explained often.
Evan Carroll
2010-09-24 17:09:56
+4
A:
You can do like this:
if(typeof variable_here == 'undefined'){
// your code here.
};
Sarfraz
2010-04-15 18:14:35
@sadmicrowave: It checks whether an object is set or not (undefined), see more info about it, i have posted the links for that in my answer. Thanks :)
Sarfraz
2010-04-15 18:25:07
@Sarfraz - I dont think that was me....but thanks for answering my question
sadmicrowave
2010-04-15 19:03:54
That will only identify the undefined, not the 'null', this is not the correct answer.
M28
2010-04-15 20:10:35
A:
jQuery attr() function returns either a blank string or the actual value (and never null or undefined). The only time it returns undefined is when your selector didn't return any element.
So you may want to test against a blank string. Alternatively, since blank strings, null and undefined are false-y, you can just do this:
if (!EmpName) { //do something }
Chetan Sastry
2010-04-15 18:20:06