How to make map in JavaScript change the object key

Question

I have the following input data:

var persons = [
    {firstname : "Malcom", lastname: "Reynolds"},
    {firstname : "Kaylee", lastname: "Frye"},
    {firstname : "Jayne", lastname: "Cobb"}
];

I need to change the value of the key in every object so expected output data is:

persons = [
    {fn : "Malcom", lastname: "Reynolds"},
    {fn : "Kaylee", lastname: "Frye"},
    {fn : "Jayne", lastname: "Cobb"}
];

I am using map function in JavaScript but it is not working.

persons.map(x => x.firstname=x.fn);

do you want to change the existing objects or a new array with new objects? — Nina Scholz
– Nina Scholz, Commented Sep 24, 2018 at 12:51
i need new array or whatever but output should like above key must be change in efficient way — Hemanth SP
– Hemanth SP, Commented Sep 24, 2018 at 12:53

MysterX · Accepted Answer · 2018-09-24 12:52:58Z

2

Your thoughts was right but need to be a little bit changed:

persons = persons.map((x) => {
  return {
    fn : x.firstname,
    lastname : x.lastname
  }
})

answered Sep 24, 2018 at 12:52

MysterX

2,3781 gold badge14 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nina Scholz · Accepted Answer · 2018-09-24 13:04:32Z

2

You could use a destructuring assignment with rest parameters ... for objects. Then map the new property with the rest properties.

This proposal works only with newer JS or with babeljs.

var persons = [{ firstname : "Malcom", lastname: "Reynolds" }, { firstname : "Kaylee", lastname: "Frye" }, { firstname : "Jayne", lastname: "Cobb" }];

console.log(persons.map(({ firstname: fn, ...rest }) => ({ fn, ...rest })));

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Sep 24, 2018 at 13:04

answered Sep 24, 2018 at 12:57

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Comments

kemicofa · Accepted Answer · 2018-09-24 12:52:52Z

1

Use map like so by returning a new object.

var persons = [
    {firstname : "Malcom", lastname: "Reynolds"},
    {firstname : "Kaylee", lastname: "Frye"},
    {firstname : "Jayne", lastname: "Cobb"}
];

const newPersons = persons.map(person=>({fn:person.firstname, ln:person.lastname}));

console.log(newPersons);

answered Sep 24, 2018 at 12:52

kemicofa

17.7k10 gold badges93 silver badges145 bronze badges

Comments

Tu Nguyen · Accepted Answer · 2018-09-24 12:53:25Z

1

Try this:

let persons = [
    {firstname : "Malcom", lastname: "Reynolds"},
    {firstname : "Kaylee", lastname: "Frye"},
    {firstname : "Jayne", lastname: "Cobb"}
];

let newPersons = persons.map(person => {
    return ({
       fn: person.firstname, lastname: person.lastname
    })
})

The newPersons array will be exactly the array that you need. Btw, I'm using let instead of var.

answered Sep 24, 2018 at 12:53

Tu Nguyen

10.2k4 gold badges30 silver badges53 bronze badges

Comments

Ankit Agarwal · Accepted Answer · 2018-09-24 12:53:26Z

1

Use forEach():

var persons = [
    {firstname : "Malcom", lastname: "Reynolds"},
    {firstname : "Kaylee", lastname: "Frye"},
    {firstname : "Jayne", lastname: "Cobb"}
];

persons.forEach((obj)=>{
  obj.fn = obj.firstname;
  delete obj.firstname;
});
console.log(persons);

answered Sep 24, 2018 at 12:53

Ankit Agarwal

30.8k5 gold badges41 silver badges63 bronze badges

Comments

protoproto · Accepted Answer · 2018-09-24 12:55:03Z

1

Use as follow:

var persons = [
    {firstname : "Malcom", lastname: "Reynolds"},
    {firstname : "Kaylee", lastname: "Frye"},
    {firstname : "Jayne", lastname: "Cobb"}
];
var result = persons.map(current => { 
    var obj = {};
    obj.fn = current.firstname;
    obj.lastname = current.lastname;
    return obj;
  });
console.log(result);

answered Sep 24, 2018 at 12:55

protoproto

2,0991 gold badge15 silver badges15 bronze badges

Comments

Mario · Accepted Answer · 2018-09-24 13:03:21Z

1

You can also use reduce

// Given
const persons = [
    {
        firstname: "Malcom",
        lastname: "Reynolds"
    },
    {
        firstname: "Kaylee",
        lastname: "Frye"
    },
    {
        firstname: "Jayne",
        lastname: "Cobb"
    }
];

// When
const people = persons.reduce((previousValue, currentValue) => {
    previousValue.push({fn: currentValue.firstname, lastname: currentValue.lastname});

    return previousValue;
}, []);

// Then
console.log(people);

answered Sep 24, 2018 at 13:03

Mario

5,0044 gold badges42 silver badges65 bronze badges

Collectives™ on Stack Overflow

How to make map in JavaScript change the object key

7 Answers 7

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related