JS If Condition of Undefined

Question

I have a user database like this:

const user = {
  subscription: {
    plan: 'free_trial',
  },
};

I need to check some condition before user changes plan.

const currentDate = new Date();
if (user.subscription.trialExpDate > currentDate) {
  // do something
} else {
  // trialExpDate is either undefined or <= currentDate
  user.subscription.trialExpDate = currentDate;
}

My question is, for some users trialExpDate will be undefined. Is it okay to compare undefined against currentDate object? Or do I need to check if trialExpDate exist first?

What is user.subscription.trialExpDate ? Is it a string ? Try new Date(user.subscription.trialExpDate) — Rayon
– Rayon, Commented Oct 2, 2016 at 3:33
user.subscription.trialExpDate is either undefined OR a date object — cocacrave
– cocacrave, Commented Oct 2, 2016 at 3:34
undefined > new Date(); will always be false.. I would have tested the value before comparing.. — Rayon
– Rayon, Commented Oct 2, 2016 at 3:36
yeah that was my question. so you would test if it's undefined first before doing the rest of the code? even if it returns same answer and shorter code? — cocacrave
– cocacrave, Commented Oct 2, 2016 at 3:38
I certainly would have tested it.. That would make my code more readable.. — Rayon
– Rayon, Commented Oct 2, 2016 at 3:39

kernal_lora · Accepted Answer · 2016-10-02 03:42:30Z

3

I would suggest check with hasownproperty. Sample:

if (user.subscription.hasOwnProperty('trialExpDate') && user.subscription.trialExpDate > currentDate) {
  // do something
} else {
  // trialExpDate is either undefined or <= currentDate
  user.subscription.trialExpDate = currentDate;
}

edited Oct 2, 2016 at 3:42

answered Oct 2, 2016 at 3:38

kernal_lora

1,1553 gold badges13 silver badges26 bronze badges

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

4 Comments

cocacrave Over a year ago

Thanks I'll do that instead :)

Rayon Over a year ago

trialExpDate is not ownProperty of user object, it belongs to user.subscription

Rayon Over a year ago

What if user.subscription.trialExpDate is null ? It will return hasOwnProperty true.. I will go with if(user.subscription.trialExpDate && .....)

kernal_lora Over a year ago

Yes, @Rayon that is one scenario. If we are confident that won't be null we can use hasownproperty otherwise your we have to check as you said

Rax Weber · Accepted Answer · 2016-10-02 03:45:20Z

1

You can just check if it is null.

if (user.subscription.trialExpDate != null || user.subscription.trialExpDate > currentDate) {
    // do something
}
else {
    // do something else
}

The variable != null will simultaneously check if the variable is null or undefined.

edited Oct 2, 2016 at 3:45

answered Oct 2, 2016 at 3:41

Rax Weber

3,78121 silver badges30 bronze badges

3 Comments

Rax Weber Over a year ago

You can read more here: stackoverflow.com/questions/2647867/…

Rayon Over a year ago

What if user.subscription.trialExpDate is 0 ? I would have had a function to test if it is a valid Date..

Rax Weber Over a year ago

Then he could check as well if it is indeed 0.

Community · Accepted Answer · 2017-05-23 12:08:59Z

In short: if you're sure that user.subscription.trialExpDate cannot be a null, using your original code is very okay.

See how the JavaScript relational comparison operators coerce types.

If user.subscription always exist and it is always an object, comparison between a Date object, and an undefined or a NaN, is evaluated as false. However, for a null, it is evaluated as +0, thus null < (new Date) will be true, null > (new Date) will be false.

When JavaScript relational comparison works,

A Date object is converted to its timestamp, which is (The Date object).valueOf().
A primitive is converted to a number, which means:
- an undefined is converted to a NaN;
- a null is converted to +0.
Then the comparison is performed between each item as you'd expect for the operator. Note that any comparison involving a NaN evaluates to false.

Collectives™ on Stack Overflow

JS If Condition of Undefined

3 Answers 3

4 Comments

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related