How can i add fields inside empty array?

Question

Good morning guys

I have to create a new JSON object array using the user array but when I do this getting the below error. could someone help me here? or help me to understand the mistake?

var users = [{ "name":"John", "age":30, "car":"fiat" },{ "name":"Raj", "age":28, "car":"hundai" }];

var allUser =[]

for (var i = 0; i < users.length; i++) {
  test(i, users[i])
}
console.log(allUser)

function test(i, user) {
  console.log(i)
  <!-- allUser.push({"username":user.name}); -->

  allUser[i].username = user.name;
  //allUser[i].userage = user.age;
  //allUser[i].usercar = user.car;
}

Expected Result:

all user should be like this

[{ "username":"John", "userage":30 },{ "username":"Raj", "userage":28 }]

allUser has a single item. Getting allUser[i] is using the indexes from users, so with i = 1, allUser[1] produces undefined. — VLAZ
– VLAZ, Commented Jan 29, 2021 at 17:57
how can I get all users like this [{ "username":"John", "userage":30 },{ "username":"Raj", "userage":28 }] — its me
– its me, Commented Jan 29, 2021 at 18:00
Option 1 - remove  Option 2 From an array of objects, extract value of a property as array + How to get a subset of a javascript object's properties — VLAZ
– VLAZ, Commented Jan 29, 2021 at 18:04
There is no problem. Either uncomment the line that will add items to allUsers or use .map. I've pointed you to two resources for how to use .map to get a subsection of the keys of an object. — VLAZ
– VLAZ, Commented Jan 29, 2021 at 18:16

3limin4t0r · Accepted Answer · 2021-01-29 18:35:42Z

3

Your test function can be fixed in the following manner:

var users = [
  { "name": "John", "age": 30, "car": "fiat"   },
  { "name": "Raj",  "age": 28, "car": "hundai" },
];

var allUser = [];

for (var i = 0; i < users.length; i++) {
  test(i, users[i]);
}
console.log(allUser);

function test(i, user) {
  allUser[i] = {}; // create and assign a new object to `allUser[i]`
  allUser[i].username = user.name;
  allUser[i].userage = user.age;
  allUser[i].usercar = user.car;
}

However the above looks over complicated, and a map call would simplify things a lot.

var users = [
  { "name": "John", "age": 30, "car": "fiat"   },
  { "name": "Raj",  "age": 28, "car": "hundai" },
];

var allUser = users.map((user) => ({
  username: user.name,
  userage: user.age,
  usercar: user.car,
}));

console.log(allUser);

answered Jan 29, 2021 at 18:35

3limin4t0r

21.4k3 gold badges38 silver badges61 bronze badges

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

Comments

Ajit Hingmire · Accepted Answer · 2021-01-30 09:21:58Z

Please check the fiddle for solution. https://jsfiddle.net/gczwk2jf/ Your alluser array is empty array, when you try to get value by a[i] e.g. a[0] or a[1], it is undefined. You are trying to access username of undefined value hence you have an error. Best way is to map or compose your complete object and assign it your array index.

allUser[i] = {
username: user.name,
userage: user.age
}

With map, you can replace the entire code with following couple of lines

var users = [{ "name":"John", "age":30, "car":"fiat" },{ "name":"Raj", "age":28, "car":"hundai" }];
var allUser = users.map(user => return {
username: user.name,
userage: user.age
});

Map is a higher order function that doesn't mutate your original array, which means you get a new array after map, keeping original user array unchanged.

CodeOfLife · Accepted Answer · 2021-01-29 18:33:16Z

1

var users = [{ "name":"John", "age":30, "car":"fiat" },{ "name":"Raj", "age":28, "car":"hundai" }];

var allUser =[]

for (var i = 0; i < users.length; i++) {
  test(i, users[i])
}
console.log(allUser)

function test(i, user) {
var data={}

  data["username"]=user["name"];
  data["userage"]=user["age"]
  allUser.push(data);

}

using map function

var users = [{ "name":"John", "age":30, "car":"fiat" },{ "name":"Raj", "age":28, "car":"hundai" }];

var allUser =[]

users.map((element)=>{
test(element)
})
console.log(allUser)

function test(user) {
var data={}

  data["username"]=user["name"];
  data["userage"]=user["age"]
  allUser.push(data);

}

Please try this.

edited Jan 29, 2021 at 18:33

answered Jan 29, 2021 at 18:15

CodeOfLife

3331 gold badge3 silver badges14 bronze badges

Collectives™ on Stack Overflow

How can i add fields inside empty array?

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related