How to add the same format of JSON object into an Array with different values?

Question

I'd like to make a JSON list with different values.

Here's the code that I am trying to do.

...
// This will contain different JSON data of friendObj
var friendList = [];

// It is just default format of JSON obj.
var friendObj={
    name: "Kim",
    age: "19",
    country: "Korea"
}

// Nodejs Router
router.post("/...", function(req,res,next){
    friendList = getFriendList(10);
    ...
});

// a function to get dump data.
fun getFriendList(n){
    var list = [];

    for (var i = 0 ; i < n ; i++){
        list.push(friendObj);
        list[i].name = "Lee";

        // This will save different ages each loop.
        list[i].age = i+20;
        list[i].country = "America";
    }

    return list;
}

When I print it out, I get the friendObj with the same values with the last element. In this case, all the element would have Lee, 39, America.

But I want different values on each element.

What should I do?

Answer 1

You created the object outside the loop, so you pushed the same object to the array multiple times. Create the object inside the loop instead:

for (var i = 0; i < n; i++) {
  var friendObj = {
    name: "Kim",
    age: "19",
    country: "Korea"
  }
  list.push(friendObj);

If you're assigning new values each iteration, it would make more sense to just come up with those values and then create the object:

for (var i = 0; i < n; i++) {
  const name = // ...
  const age = // ...
  const country = // ...
  list.push({ name, age, country });

Answer 2

List elements are reference the same Object (friendObj)

Check about immutable object

function getFriendList(n){
  var list = [];

  for (var i = 0 ; i < n ; i++){
      list.push(Object.assign({}, friendObj)); // Different object ref
      list[i].name = "Lee";

      // This will save different ages each loop.
      list[i].age = i+20;
      list[i].country = "America";
  }

  return list;
}

You can create immutable object with Object.assign, Object.freeze, Spread syntax, ...etc

Answer 3

This is because the same friendObj is pushed into the loop on each iteration. Each element of the array is now holding reference to the same object.

Change list.push(friendObj); inside for loop to list.push({...friendObj});. This will create a copy of the friendObj and push that copy into the array.

Note this is only a shallow copy which is fine in this case since the friendObj is not deeply nested.

Answer 4

You can try this code

I just change the little bit more technic. maybe it helps your problem solve.

  const friendList = [];

  // It is just default format of JSON obj.
  const friendObj = [
    {
      name: 'Kim',
      age: '19',
      country: 'Korea',
    },
    {
      name: 'alam',
      age: '36',
      country: 'dhaka',
    },
    {
      name: 'name3',
      age: '30',
      country: 'usa',
    },
    {
      name: 'name9',
      age: '25',
      country: 'Bangladesh',
    },
    {
      name: 'name20',
      age: '25',
      country: 'pakistan',
    },
    {
      name: 'name30',
      age: '25',
      country: 'India',
    },
  ];

  if (friendObj !== null) {
    console.log(getFriendList(4));
  }
  // a function to get dump data.
  function getFriendList(n) {
    const list = friendObj.slice(0, n);
    list.map(item => {
      item.name = 'lee';
      item.age *= 2;
      item.country = 'Bangladesh';
    });
    return list;
  }

=== Thank you ===