Is this a good way to check for undefined values in javascript?

Question

I'm currently transitioning from promises to async await. And its been easier to reason about code. I just have a question on if using way to check for undefined is good. The code is being used in nodejs and checking against a database. The code goes something like this.

Edit: I am aware that I'm supposed to catch for errors. I just got lazy here.

// This is a hypothetical function
async function retrieveUser(userID){
  let user = await databasefetchfuction(userID);
  if(user) return user;
  return;
}

controller.getUser = async function(req,res){
 let user = await retrieveUser(req.params.userID);
 if(!user){ // Is this ok?
   return res.status(404).json();
 } 
 return res.status(200).json({ user });
}

I was if doing this is fine or if I should explicitly check for undefined using user === undefined?

I'm voting to close this question as off-topic because it is asking for [a code review](https://codereview.stackexchange.com/help/on-topic) — Quentin, Apr 19 '17 at 13:00
Depends really. Are any of `false`, `""`, `0`... valid return values or should they be errors too? — Niet the Dark Absol, Apr 19 '17 at 13:00
Your current form will return properly for the following values: `null`, `undefined`, `NaN`, `empty string ("")`, `0`, `false` — Tyler Roper, Apr 19 '17 at 13:01
Isn't the real question will this check if my method returned a value? What do these methods do exactly? The result will depend on that. — Liam, Apr 19 '17 at 13:03
@Quentin I'm not really asking for a code review. The purpose of the code was to show an example. This code is fictitious. I just want to confirm behaviour. — , Apr 19 '17 at 13:03

score 2 · Accepted Answer · edited May 23 '17 at 12:25

2

if(!user) is fine as long as you are willing to accept that it will be true for all the other "falsey" things in JS.

See this: All falsey values in JavaScript

edited May 23 '17 at 12:25

Community

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answered Apr 19 '17 at 13:01

gforce301

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This explanation will suffice. Thank! – Apr 19 '17 at 13:06

score 0 · Answer 2 · answered Apr 19 '17 at 13:00

0

Using !var is perfectly fine in the case of a database return. There is no way that a user was found but !var returns true.

answered Apr 19 '17 at 13:00

itsundefined

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score 0 · Answer 3 · answered Apr 19 '17 at 13:01

0

The undefined value in JavaScript is treated as a falsy value, so yes - you are doing it in a proper way. If you want to check other field in user object, you should check both user and user.property.

answered Apr 19 '17 at 13:01

TheOpti

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Is this a good way to check for undefined values in javascript?

3 Answers3