JavaScript Object. Change key name of objects in array

Question

I have an array of objects like this example:

[
  { id: 44, message: 'abcd', name: 'example1' },
  { id: 44, message: 'efgh', name: 'example2' },
  { id: 45, message: 'ijkl', name: 'example3' },
  { id: 45, message: 'mnop', name: 'example4' },
]

As you can see the, id value is repeated. Now i need change key name of "name" to "lastName" only at second repeated object:

[
  { id: 44, message: 'abcd', name: 'example1' },
  { id: 44, message: 'efgh', lastName: 'example2' },
  { id: 45, message: 'ijkl', name: 'example3' },
  { id: 45, message: 'mnop', lastName: 'example4' },
]

Welcome to Stackoverflow. What have you tried so far to solve this issue? Where did you get stuck? — fjc, Apr 27 '20 at 19:06
I think this has already been answered [here](https://stackoverflow.com/questions/4647817/javascript-object-rename-key) — AJ_, Apr 27 '20 at 19:13
Tranks, i stored on a variable the key name, but i got stuck when i search the object that id is repeated. — jspdev, Apr 27 '20 at 19:14

xdeepakv · Accepted Answer · 2020-04-27T19:20:37.643

You can keep last id track, and modify the return object in map loop

For unsorted list:

let data = [
  { id: 44, message: "abcd", name: "example1" },
  { id: 44, message: "efgh", name: "example2" },
  { id: 45, message: "ijkl", name: "example3" },
  { id: 45, message: "mnop", name: "example4" },
];
let idMap = new Set();
const result = data.map((item) => {
  if (idMap.has(item.id)) {
    const { name: lastName, ...rest } = item;
    item = { ...rest, lastName };
  } else {
    idMap.add(item.id);
  }
  return item;
});
console.log(result);

Note: data has to be sorted based on id.

let data = [
  { id: 44, message: "abcd", name: "example1" },
  { id: 44, message: "efgh", name: "example2" },
  { id: 45, message: "ijkl", name: "example3" },
  { id: 45, message: "mnop", name: "example4" },
];
let lastId = "";
const result = data.map((item) => {
  if (lastId === item.id) {
    const { name: lastName, ...rest } = item;
    item = { ...rest, lastName };
    lastId = "";
  } else {
    lastId = item.id;
  }
  return item;
});

console.log(result);

score 0 · Answer 2 · answered Apr 27 '20 at 19:12

You can save the ids of each item and rename the key from name to lastName if the item with this id was already visited.

let list = [
            { id: 44, message: 'abcd', name: 'example1' },
            { id: 44, message: 'efgh', name: 'example2' },
            { id: 45, message: 'ijkl', name: 'example3' },
            { id: 45, message: 'mnop', name: 'example4' },
           ];
let checked = [];
list.forEach(function (item) {
     if(checked.includes(item.id)){
          item['lastName'] = item['name'];
          delete item['name'];
     }else{
          checked.push(item.id);
     }
});
console.log(list)

JavaScript Object. Change key name of objects in array

2 Answers2