I am trying to check if a variable exists using a function

Asked Nov 25 '16 at 06:51

Active Nov 25 '16 at 07:36

Viewed 44 times

I am trying to check if a variable exists using a function but somehow this doesn't work, can somebody help me, thanks a lot!

// console returns false and is expected
if(typeof aaaaaaa !== 'undefined'){
  console.log(true);
}else{
  console.log(false);
}

=============================================

// console returns 'aaaaaaa is not defined', and stops my code
function checkExist(arg){
    if(typeof arg !== 'undefined'){
        console.log(true);
    }else{
        console.log(false);
    }
}
checkExist(aaaaaaa);

it's just different than JavaScript check if variable exists (is defined/initialized)

edited May 23 '17 at 12:30

Community

asked Nov 25 '16 at 06:51

Fu-Han Zhang

could done better like this if(typeof aaaaaaa !== void(0)) or if(aaaaaaa !== void(0)) – Álvaro Touzón Nov 25 '16 at 06:53
that is expected, as when you are calling checkExist(aaaaaaa) , it is trying to find the reference to aaaaa so it can be passed on to the method. Where as in the earlier case, you are just trying to read the type of a variable that doesn't exist and it works. – Sreekanth Nov 25 '16 at 06:55
remove `aaaaaaa` from `checkExist(aaaaaaa);` – Mahi Nov 25 '16 at 06:55
I would add "typeof aaaaaaa !== 'undefined' || aaaaaaa !== null" to make sure the null values aren't passed – Marcus Höglund Nov 25 '16 at 06:57
Just use theObject.HasOwnProperty("aaaaaaa") – Klinger Nov 25 '16 at 06:58
if(typeof (aaaaaaa) !== 'undefined') mind the () for 'typeof' – Damitha Shyamantha Nov 25 '16 at 06:59
If you are in strict mode, it's completely correct that it stops your code, as you have a syntax error – Icepickle Nov 25 '16 at 08:21

I am trying to check if a variable exists using a function

0 Answers0