JavaScript condition always fails

Question

In the below code, the if statement always fails. New to JavaScript, couldn't figure out.

I believe the code is self explanatory. What am I doing wrong?

if (localStorage.user_name === null || localStorage.user_name === 'undefined') {
    registerUser(userName);
} else {
    login(localStorage.user_name);  // Gets executed always... Even if there is no user_name in localStorage.
}

`null ` and `undefined` are falsy. You needn't check them explicitly. Try with - `if (localStorage.user_name) { ..// code }` — Pramod Karandikar, Jan 30 '15 at 07:34
I think you can use this -> http://dorey.github.io/JavaScript-Equality-Table/ — sarveshseri, Jan 30 '15 at 07:35
btw `undefined` is not a string, if you would to check if some is undefined you should use `typeof localStorage.user_name === 'undefined'` — zb', Jan 30 '15 at 07:37
`===` is very specific comparison. Is failing because `localStorage.user_name` is neither `null` nor `undefined`. — sarveshseri, Jan 30 '15 at 07:37

score 1 · Accepted Answer · answered Jan 30 '15 at 07:35

1

The problem is in your second condition. Since you're using ===, and comparing with 'undefined' which is a string, instead of undefined, it returns false. So, you need localStorage === undefined, as in

if (localStorage.user_name === null || localStorage.user_name === undefined)

Or, need to use typeof which returns String. But there's a better way

if(!localStorage.user_name){

}

answered Jan 30 '15 at 07:35

Amit Joki

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NO, using == is not right way....it is comparing like `undefined=='undefined'`...which is not true. – Vijay Jan 30 '15 at 07:43
@GokulNath its not wrong as it is being typecasted. – Amit Joki Jan 30 '15 at 07:43
@Vijay nope. It's right. You need to look up on that for why. – Amit Joki Jan 30 '15 at 07:43
I got it...it is working because of first condition. `undefined==null` is true while `undefined===null` is false. – Vijay Jan 30 '15 at 07:46

JavaScript condition always fails

1 Answers1