JS - conditional property selection

Question

I have two arrays with the following structure:

First dictionary:

 [{id: 111, abbr: "FBI", name: "Federal Burreau of Investigation"},
 {id: 59, abbr: "CIA", name: "Central Intelligence Agency"},
 {id: 130, abbr: "EU", name: "European Union"}]

Second dictionary:

 [{id: 28, name: "Administration"},
 {id: 107, name: "Advocacy"},
 {id: 100, name: "Agriculture"},
 {id: 77, name: "Air & Aviation"}]

I am trying to create a delimiter function that accesses these objects in the following way:

 finalDictionary.push({ delimiter: dictionary[0].abbr.charAt(0) });

and correspondingly:

 finalDictionary.push({ delimiter: dictionary[i].name.charAt(0) });

My aim is to make the method universal and diminish the amount of final code. As you see, the only difference here is the property by which I am accessing the dictionary, 'abbr' and 'name'. I tried to do it the following way:

 var ext = (name === 'agencies') ? 'abbr' : 'name';
 finalDictionary.push({ delimiter: dictionary[i].ext.charAt(0) });

However, I get an error:

 TypeError: Cannot read property 'charAt' of undefined

The question is how can I conditionally access the object property? Maybe, there is a better approach than this one? If not, what am I doing wrong?

This is my first question on SO, pardon me in case I failed to comply with the regulations. — Eugene, Nov 15 '18 at 12:07
What is `i`, and which dictionary is `dictionary`? Can you post a [MCVE], ideally in a live snippet in your question? — CertainPerformance, Nov 15 '18 at 12:08
Possible duplicate of https://stackoverflow.com/questions/4244896/dynamically-access-object-property-using-variable — misorude, Nov 15 '18 at 12:11
@CertainPerformance Sorry, next time I will. SO looks like a pretty sophisticated resource in terms of politics :) — Eugene, Nov 15 '18 at 12:18

score 4 · Accepted Answer · answered Nov 15 '18 at 12:10

4

The problem is in this line:

dictionary[i].ext.charAt(0)

dictionary[i].ext assume that you have a property ext inside dictionary[i] which you don't and therefore it returns undefined.

than what happens is undefined.charAt(0) which raises your error

Change it to:

dictionary[i][ext].charAt(0)

Than the property here is the value of ext which is 'abbr' or 'name'

answered Nov 15 '18 at 12:10

omri_saadon

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Thank you, this is it! I should have used bracket notation to access the property via string which I get as a result of my ternary. Appreciated :) – Eugene Nov 15 '18 at 12:17
This is a matter of 2 more minutes :) – Eugene Nov 15 '18 at 12:20

score 0 · Answer 2 · answered Nov 15 '18 at 12:12

0

There is no property named ext in the example json you have shown, that is why you are facing this error.

answered Nov 15 '18 at 12:12

codeLover

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Ext is a variable storing the name of the property to be used, I am getting it via a ternary – Eugene Nov 15 '18 at 12:19

JS - conditional property selection

2 Answers2