Checking undefined value not working?

Question

I have the following javascript code:

var currentIds = localStorage.getItem('currentPairsIds');

if ((typeof currentIds === "undefined") ||
    (currentIds == null))
        $.myNameSpace.currentIDs = new Array(3);
    else
        $.myNameSpace.currentIDs = currentIds.Split(',');

I'm debugging with Firebug and although currentIds hasn't got any value it always executes else statement.

UPDATE:

I'm getting this value from HTML5 storage.

What am I doing wrong?

Well that must mean that the value of currentIds is not really undefined. — Pointy
– Pointy, Commented Jun 9, 2011 at 15:56
@Pointy: it's undefined. The statement $.myNameSpace.currentIDs = currentIds.Split(','); throws an exception. — VansFannel
– VansFannel, Commented Jun 9, 2011 at 15:59
Is currentIds "undefined" or is it undefined? typeof "undefined" is string. — Linus Kleen
– Linus Kleen, Commented Jun 9, 2011 at 15:59
Either you are stuck in an alternate universe, or the value of currentIds isn't what you think it is. — Andrew
– Andrew, Commented Jun 9, 2011 at 16:05

VansFannel · Accepted Answer · 2011-06-10 06:14:44Z

10

This is how I have solved my problem:

var currentIds = localStorage.getItem('currentPairsIds');

if ((currentIds === undefined) ||
    (currentIds == null) || (currentIds == "undefined"))
        $.myNameSpace.currentIDs = new Array(3);
    else
        $.myNameSpace.currentIDs = currentIds.split(',');

localStorage.getItem('currentPairsIds'); returns the string "undefined".

There is another error in Split() function. The right version is without any capital letter.

edited Jun 10, 2011 at 6:14

answered Jun 10, 2011 at 5:47

VansFannel

46.1k119 gold badges381 silver badges656 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Ruan Mendes Over a year ago

This is wrong, localStorage.getItem() does not return the string "undefined", it returns null, you only need the null check, not the other stuff that you're blindly testing.

Dave Alperovich Over a year ago

@JuanMendes, i got an undefined and this syntax worked for my problem. In fact, it was the odd == "undefined" that caught my problem!

Ruan Mendes Over a year ago

@DaveA That is because you saved something that was undefined, and local storage converts it into the string "undefined". When saving something into localStorage, you should be careful not to set it to undefined, or null. I would always set it to the empty string instead

Dave Alperovich Over a year ago

@JuanMendes, i did indeed save invalid data. App is in early development and sloppy things happen. But I don't think the string "undefined" went into memory. But things like this will happen. You can kill yourself with validation, but issues will crawl past you...

Ruan Mendes Over a year ago

@DaveA localStorage.setItem('test', undefined) will cause localStorage.getItem('test') to return 'undefined', the string. That can easily happen if you set it to a falsy value . That's what you should avoid

|

maerics · Accepted Answer · 2011-06-09 16:28:58Z

2

I would use a direct comparison instead of the notoriously odd "typeof" operator:

if ((currentIds === undefined) || (currentIds === null)) {
  //...

edited Jun 9, 2011 at 16:28

answered Jun 9, 2011 at 16:06

maerics

157k47 gold badges277 silver badges299 bronze badges

Comments

Ruan Mendes · Accepted Answer · 2011-06-09 16:41:06Z

2

It's not working because localStorage.getItem returns null if the item is not defined, it does not return undefined http://dev.w3.org/html5/webstorage/#dom-storage-getitem

Example: http://jsfiddle.net/mendesjuan/Rsu8N/1/

var notStored = localStorage.getItem('ffff');

alert(notStored); // null
alert(typeof notStored); // object, yes, null is an object.

Therefore you should just be testing

alert(notStored === null);

answered Jun 9, 2011 at 16:41

Ruan Mendes

92.7k31 gold badges161 silver badges225 bronze badges

Comments

Nik Sumeiko · Accepted Answer · 2011-06-09 16:02:16Z

0

I think you have to make checking for undefined comparing with == instead of ===. Example:

typeof currentIds == "undefined"

This will make sure, the variable is really undefined or not.

answered Jun 9, 2011 at 16:02

Nik Sumeiko

8,8419 gold badges52 silver badges53 bronze badges

2 Comments

MooGoo Over a year ago

== or === makes no difference in this case.

Andrew Over a year ago

That changes nothing, typeof returns a String.

Community · Accepted Answer · 2017-05-23 12:16:09Z

0

[Edit Edit Edit Edit :P]

currentIds = "undefined"

implies

typeof currentIds == "String"

Also see, Detecting Undefined, === isn't necessary for string comparison.

edited May 23, 2017 at 12:16

CommunityBot

11 silver badge

answered Jun 9, 2011 at 15:57

Andrew

13.9k14 gold badges70 silver badges85 bronze badges

6 Comments

Andrew Over a year ago

Your code is correct, the value of currentIDs as you described it doesn't seem to match what you expect it to be, the problem is somewhere else.

VansFannel Over a year ago

I've updated my question this line var currentIds = localStorage.getItem('currentPairsIds'); It's where I'm getting currentIds value.

Andrew Over a year ago

@VansFannel you are retrieving an array then trying to call split on it, which is undefined.

VansFannel Over a year ago

Your previous answer is the correct answer. localstorage.getItem returns the string "undefined". I have to check if currentIds == "undefined".

VansFannel Over a year ago

@Andrew: But I've solved using currentIds == "undefined". Your answer said currentIds = "undefined".

|

bthn · Accepted Answer · 2019-11-12 09:44:56Z

0

In my case LocalStorage.getItem() was converting it to "undefined" as string. I also needed to check if it s "undefined" as a string.

var myItem = LocalStorage.getItem('myItem');
if(myItem != "undefined" && myItem != undefined && myItem != null){
    ...
}

answered Nov 12, 2019 at 9:44

bthn

1962 silver badges16 bronze badges

Comments

qɐʇǝɥɐW · Accepted Answer · 2020-09-22 13:39:58Z

0

if( typeof(varName) != "undefined" && varName !== null )

be sure, you use ( " " ) quotes when checking with typeof()

answered Sep 22, 2020 at 13:39

qɐʇǝɥɐW

4645 silver badges21 bronze badges

Collectives™ on Stack Overflow

Checking undefined value not working?

7 Answers 7

6 Comments

Comments

Comments

2 Comments

6 Comments

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

6 Comments

Comments

Comments

2 Comments

6 Comments

Comments

Comments

Linked

Related