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, Oct 02 '16 at 03:33
`user.subscription.trialExpDate` is either `undefined` OR a `date` object — cocacrave, Oct 02 '16 at 03:34
`undefined > new Date();` will always be `false`.. I would have tested the value before comparing.. — Rayon, Oct 02 '16 at 03:36
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, Oct 02 '16 at 03:38
I certainly would have tested it.. That would make my code more readable.. — Rayon, Oct 02 '16 at 03:39

kernal_lora · Answer 1 · 2016-10-02T03:42:30.993

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 02 '16 at 03:42

answered Oct 02 '16 at 03:38

kernal_lora

1,115
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Thanks I'll do that instead :) – cocacrave Oct 02 '16 at 03:39
1

`trialExpDate` is not `ownProperty` of `user` object, it belongs to `user.subscription` – Rayon Oct 02 '16 at 03:40
1

What if `user.subscription.trialExpDate` is `null` ? It will return `hasOwnProperty` `true`.. I will go with `if(user.subscription.trialExpDate && .....)` – Rayon Oct 02 '16 at 03:42
1

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 – kernal_lora Oct 02 '16 at 03:46

Rax Weber · Answer 2 · 2016-10-02T03:45:20.227

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 02 '16 at 03:45

answered Oct 02 '16 at 03:41

Rax Weber

3,730
19
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1

You can read more here: http://stackoverflow.com/questions/2647867/how-to-determine-if-variable-is-undefined-or-null – Rax Weber Oct 02 '16 at 03:47
What if `user.subscription.trialExpDate` is `0` ? I would have had a function to test if it is a valid `Date`.. – Rayon Oct 02 '16 at 03:47
Then he could check as well if it is indeed `0`. – Rax Weber Oct 02 '16 at 03:48

score 0 · Answer 3 · edited May 23 '17 at 12:08

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.

JS If Condition of Undefined

3 Answers3