CODEWITHSUNDEEP
javascriptlocal-storageundefined
davidhq
davidhq

Reputation: 4760

ORing an undefined value from localStorage when passing arguments

If I do this:

localStorage['a'] = undefined
alert(localStorage['a'] || 20)

"undefined" is alerted - WHY?

var a = undefined
alert(a || 20)

now 20 is alerted.

localStorage.clear()
alert(localStorage['a'] || 20)

here 20 as well... and I checked localStorage['a'] is undefined... just like in the first case when I set it to undefined manually... so why different results?

Upvotes: 2

Views: 301

Answers (1)

Denys Séguret
Denys Séguret

Reputation: 382454

localStorage stores strings and converts what you pass to strings, so

localStorage['a'] = undefined

sets the string "undefined" as value in localStorage. It doesn't remove the key and it doesn't set its value as undefined.

And of course "undefined" isn't falsy so "undefined"||20 is "undefined".

To remove a value, use

localStorage.removeItem('a');

As an aside be careful to the fact that if you set 

localStorage['a'] = 20

then you don't get 20 when calling localStorage['a'] but the string "20". When you want to get a not null number with a default value, you may do this :

var num = parseInt(localStorage['a'])||20;

Upvotes: 5

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