Writing Ternary Expression to Match Specific If/Else in JavaScript

Question

In doing an ETL to get data from a Sybase database into a MongoDB backend, I can do this:

if (data.hire_date) staffProfile.hireDate = data.hire_date;

This method prevents nulls from being populated into the MongoDB. If data.hire_date has a value, then it will be dropped into staffProfile.hireDate. However, if there is no value, it effectively is ignored.

Now, I'd like to create the same result with a ternary expression. Something like:

staffProfile.hireDate = data_hireDate ? data_hireDate : null;

However, I don't want to use null here, because when I do that I end up with a bunch of nulls in the database. My question really boils down to two things: what is effectively happening in my first example, with the "if" case, when the value is not found? Is the result undefined? What could I use in the ternary syntax example to effectively write the same conditional check - right through to what is passed when the value doesn't exist?

Would this be the equivalent expression to my first example?

staffProfile.hireDate = data_hireDate ? data_hireDate : undefined;

staffProfile.hireDate: staffProfile.hireDate ? This syntax doesn't make sense - the colon should come after the question mark in a ternary, not before — CertainPerformance
– CertainPerformance, Commented Oct 13, 2018 at 0:31
If you don't define it, it's undefined. What the DB and/or your code expects if there's no value, only you know that. — Dave Newton
– Dave Newton, Commented Oct 13, 2018 at 0:32

P.S. · Accepted Answer · 2018-10-13 00:44:26Z

1. "What is effectively happening in my first example, with the "if" case, when the value is not found? Is the result undefined?"

Yes, it will be undefined, if the condition doesn't get passed, and the object property is not created and nothing's assigned to it:

const data = {};
const staffProfile = {};

if (data.hire_date) staffProfile.hireDate = data.hire_date;

console.log("data:", data);
console.log("staffProfile.hireDate:", staffProfile.hireDate);

2. "What could I use in the ternary syntax example to effectively write the same conditional check - right through to what is passed when the value doesn't exist?"

You can achieve absolutely the same result this way:

const data = {};
const staffProfile = {};

data.hire_date ? staffProfile.hireDate = data.hire_date : null;

console.log("data:", data);
console.log("staffProfile.hireDate:", staffProfile.hireDate);

And not this way (it will become null in this case):

const data = {};
const staffProfile = {};

staffProfile.hireDate = data.hire_date ? data.hire_date : null;

console.log("data:", data);
console.log("staffProfile.hireDate:", staffProfile.hireDate);

Kyaw Siesein · Accepted Answer · 2018-10-13 00:40:59Z

0

if date_hireDate exits, it will be assigned to staffProfile.hireDate. The below syntax is what you want.

staffProfile.hireDate = data_hireDate && data_hireDate

However, it does not make sense. date_hireDate before && operator should be a condition like date_hireDate === something.

answered Oct 13, 2018 at 0:40

Kyaw Siesein

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