Modify JavaScript object property from array to string

Question

I have a JavaScript object where one of the properties is an array. I want to modify that object to create an almost identical object, except that one property is a String instead.

Looks like the join method can be used to change an array to a String (e.g., console.log(elements.join('-'))).

But how do I create a new object that's identical to the old object, but with one property different (i.e., a string instead of an array)?

For example, I have this object, carOriginal:

{
  "make": "Ford",
  "model": "F150",
  "features": [
    "windows",
    "seatbelts"
  ]
}

... and from that I want to create this object, carNew:

{
  "make": "Chevy",
  "model": "Tahoe",
  "features": "windows,seatbelts"
}

Just to confirm I'm understanding your question correctly, you want to keep the original variable as well as create a new object in its own right, and not just overwrite the existing object, correct? — Jeffrey
– Jeffrey, Commented Jul 16, 2019 at 21:50

charlietfl · Accepted Answer · 2019-07-16 21:51:45Z

2

If using ES6 you can destructure the original and add new features value :

const data = {
  "make": "Ford",
  "model": "F150",
  "features": [
    "windows",
    "seatbelts"
  ]
}


const other = {...data, features: data.features.join()}

console.log(other)

answered Jul 16, 2019 at 21:51

charlietfl

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1 Comment

Patrick Roberts Over a year ago

I don't think object spread syntax was added until later in ES2018. ES2015 only supported iterable spread and rest syntax.

DanieleAlessandra · Accepted Answer · 2019-07-16 21:57:35Z

1

If you don't know the name of the property you have to check every value to see if it is an array:

function subJoin(obj) {
    for (let prop in obj) {
        if (obj.hasOwnProperty(prop)) {
            if (Array.isArray(obj[prop])) {
                obj[prop] = obj[prop].join(',');
            }
        }
    }
    return obj;
}


let input = {
    "make": "Ford",
    "model": "F150",
    "features": [
       "windows",
       "seatbelts"
    ]
}

let output = subJoin(input);
console.log(output); /// -->  { "make": "Chevy", "model": "Tahoe", "features": "windows,seatbelts" }

answered Jul 16, 2019 at 21:57

DanieleAlessandra

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Comments

Ghoul Ahmed · Accepted Answer · 2019-07-16 21:51:57Z

0

try this:

const obj = {
  "make": "3",
  "model": "2019-07-17",
  "features": [
    "windows",
    "seatbelts"
  ]
}

const result  =  Object.assign({},obj, {features: obj.features.join()});
console.log(result);

answered Jul 16, 2019 at 21:51

Ghoul Ahmed

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Comments

Patrick Roberts · Accepted Answer · 2019-07-16 21:58:22Z

0

You can use object rest and spread syntax to collect the rest of the keys in a separate shallow copy that the modified property will be assigned to:

const carOriginal = {
  "make": "Ford",
  "model": "F150",
  "features": [
    "windows",
    "seatbelts"
  ]
};

function transform ({ features, ...keys }) {
  return { ...keys, features: features.join() };
}

const carNew = transform(carOriginal);

console.log(carNew);

edited Jul 16, 2019 at 21:58

answered Jul 16, 2019 at 21:52

Patrick Roberts

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