Why when I change x variables, the property 'friends' also change although I didn't do anything

JavaScript
1

Tell us what’s happening:
Describe your issue in detail here.
why when I change x variable, the property ‘friends’ also change simutaneously although I haven’t pass the value of x to property ‘friends’ again yet.
Thanks for helping.

  **Your code so far**


let user = {
name: 'Kenneth',
age: 28,
data: {
  username: 'kennethCodesAllDay',
  joinDate: 'March 26, 2016',
  organization: 'freeCodeCamp',
  friends: [
    'Sam',
    'Kira',
    'Tomo'
  ],
  location: {
    city: 'San Francisco',
    state: 'CA',
    country: 'USA'
  }
}
};

function addFriend(userObj, friend) {
// Only change code below this line
let x = userObj.data.friends;
x.push(friend);
return userObj.data.friends
// Only change code above this line
}

console.log(addFriend(user, 'Pete'));

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36

Challenge: Modify an Array Stored in an Object

Link to the challenge:

2

Objects and arrays will be stored using references and not by values. So try to use spread operator (ES6 feature). By using this, you will be doing a shallow copy of your object. So the main object properties won’t get effected.

function addFriend(userObj, friend) {
// Only change code below this line
let x = [...userObj.data.friends,friend];
console.log(x);
return userObj.data.friends
// Only change code above this line
}
3

Hi, the answer is simple you haven’t copied the friend’s array instead you have directly changed the values in the array as arrays and objects are stored using their reference.

4

thank you for your help

5

is that mean if I set “let x = userObj.data.friends” it’s also equal to “userObj.data.friends = x” ?

6

I got it. Thanks for your hint. Object references and copying

7

It’s like saying A = 5 it’s also equal to 5 = A they are not the same, but in let x = userObj.data.friends it won’t make any sense if you used userObj.data.friends instead of replacing it with variable x in the code. Why would someone ( beginners mistake ) assign a value to a variable and then never use it, here the variable will be called an unused variable

If you use:

function addFriend(userObj, friend) {
// Only change code below this line
let x = userObj.data.friends;
 userObj.data.friends.push(friend);
return userObj.data.friends
// Only change code above this line

Your code will definitely run, but it’s not recommended ( as it doesn’t make any sense ).

8

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