CODEWITHSUNDEEP
javascript
Lone Learner
Lone Learner

Reputation: 20628

What is the benefit of using === operator to test for undefined instead of using == operator?

I usually test whether a JavaScript variable is defined or not, using the following test:

if (typeof a == 'undefined')
    a = 'default value'

However, I have seen many people suggesting that it is safer to use the following instead:

if (typeof a === 'undefined')
    a = 'default value'

I am aware of the difference between == and === operators but I am unable to understand why typeof a == 'undefined' could be unsafe.

Could you please a scenario in which the first code example is unsafe or could lead to issues? Also, what are the advantages of using the latter syntax over the first?

Upvotes: 1

Views: 163

Answers (2)

freakish
freakish

Reputation: 56467

Since typeof a is always a string then == and === will always yield the same result, i.e. there is no significant difference between them ( the only one is that one is longer then the other ;) ).

Warning, personal opinion: I find == operator completely horrible. How could anyone think that it is a good idea to have two different comparison operators? There is no other language where two objects of different type can be equal. This is insane. Thus people tend to use === all the time, because it is a good practice. So I guess that in this situation it is just a habit... a good habit.

Upvotes: 4

bfavaretto
bfavaretto

Reputation: 71908

I am unable to understand why typeof a == 'undefined' could be unsafe

It's not unsafe, it's perfectly fine. The typeof operator is guaranteed to return a string, so you'll always be comparing two strings. The abstract equality algorithm will behave just like strict equality.

Upvotes: 6

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