How to update data via fetch for only some fields?

Question

JavaScript

Good day.
There is a fetch request:

class getData {
    fetch() {
        var data = fetch(url, myInit)
        .then(status)
        .then((data) => data.json())
        .catch((error) => {
            console.log('error', error)
    })
    return data;
    }
}

And by setTimeout there is an update

var timer = setTimeout(function tick() {
let getAPIData = new getData();

getAPIData.fetch().then(function get(data) {   
  ....
let a = Date.parse(alert.expiry);
let eta = expiry(a);
p2.innerHTML = `${eta}`;
 ....
}
timer = setTimeout(tick, 1000);
}, 100);
function expiry(ex) {
    let now = Date.now() /1000;
    let expiry = ex / 1000;
    
    let diff = expiry - now;
    let b = fortime(diff) // Просто формат даты

    return b
    
}

How to make sure that not all of the get function is updated, but only a few of its parts?
For example:
So that when updating a query, the data changes only in the eta variable

Answer 1

Pass one more parameter to it (for example, an array of variable names that need to be updated or something else ...), based on which perform the necessary actions inside the function.