How do I grab specific data dynamically from an array of objects?

Question

Situation

I have code that takes a local JSON file and parses it into an object. This part works perfectly.

My goal is to create a function that takes two parameters:

The path of the JSON file to be parsed.
The property name of a specific object so I can grab the value behind the key.

Problem

I added a variable (objectName) to pass the property name. I also added [0].fx so I can call the data from the first object only. When I run my code, I get Undefined.

Where did I go wrong?

(in the example code below, I was aiming to get "David")

const localDataObject = (fileName, objectName) => {
const localData = path.join(__dirname, "../", fileName);

fs.readFile(localData, (err, data) => {
   const objectData = JSON.parse(data);
   const fx = objectName;
        console.log(objectData[0].fx);
    });
};

localDataObject("./Family.json", "name");

the first object looks like this:

[
    {
        "name": "David",
        "age": "24",
        "role": "Studet"
    },

]

try objectData[0][objectName] or objectData[0][fx]

Someone Special
– Someone Special

2022-02-15 09:19:54 +00:00
Commented Feb 15, 2022 at 9:19 — Someone Special
– Someone Special, Commented Feb 15, 2022 at 9:19

Ghazni Ali · Accepted Answer · 2022-02-15 09:30:48Z

1

The solution for your code is :

const localDataObject = (fileName, objectName) => {
const localData = path.join(__dirname, "../", fileName);

fs.readFile(localData, (err, data) => {
   const objectData = JSON.parse(data);
   const fx = objectName;
        console.log(objectData[0][fx]);
    });
};

localDataObject("./Family.json", "name");

answered Feb 15, 2022 at 9:30

Ghazni Ali

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3 Comments

Vinn Over a year ago

Why does this work?

Ghazni Ali Over a year ago

It is because before you were using console.log(objectData[0].fx); which means it was assigning the address of fx to get the node value which is wrong and it will give you an undefined value as it does not exist. but when you change that to [fx] it means first to get the value of fx and then use it to get the node. I hope my explanation helps you.

Vinn Over a year ago

amazing. Thank you for the help Ghazni.

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