How to update javascript object

Question

I have a js object like

[{"name":"John","group":"t1..." .....}]

so to create new user from same t1, I loop through the obj using

var new_user;
for(var i=0; i<users.length; i++) {
  if(users[i].group === 'group name goes here') {
    new_user = users[i];
    break;
  }
}

then is simply push it using users.push(new_user); then I try to change the just the name using

var l = users.length - 1; users[l].name = 'Jack';

it changes the name for the all the users.

[{"name":"Jack","group":"t1..." .....},{"name":"Jack","group":"t1..." .....}]

I know I am doing something wrong. I appreciate any help.

Are you sure that all of the other elements had name other than Jack before you do users[l].name = 'Jack'? — ekad
– ekad, Commented Dec 2, 2014 at 13:36
It's not that you're doing anything wrong, but how JavaScript handles the values. See stackoverflow.com/questions/518000/… for more details... — War10ck
– War10ck, Commented Dec 2, 2014 at 13:38

Haneev · Accepted Answer · 2014-12-02 13:38:12Z

7

Problem here is that you assign the a new variable name to an old object. That is a reference and not a copy of the object. new_user = users[i] creates an reference that new_user is linked to users[i]. You have to copy the users[i] object, in order to only change the new_user. Underscore has a copy/clone function that you can use.

answered Dec 2, 2014 at 13:38

Haneev

7755 silver badges6 bronze badges

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

Comments

ekad · Accepted Answer · 2014-12-02 13:59:45Z

1

@Haneev's answer gives the concept of why the name of all users elements was changed by your code. Below is a code example of how you copy users[i] using slice method

var users = [{"name":"John","group":"t1"}];

var new_user;
for(var i=0; i<users.length; i++) {
  if(users[i].group === 't1') {
    // make a copy of users[i] and assign to new_user
    new_user = users.slice(i);
    break;
  }
}

// add new_user to users
users.push(new_user);

var l = users.length - 1; 
users[l].name = 'Jack';

alert(users[0].name); // this will display John
alert(users[1].name); // this will display Jack

Working demo: http://jsfiddle.net/hkLkkepo/

answered Dec 2, 2014 at 13:59

ekad

14.7k26 gold badges46 silver badges49 bronze badges

Collectives™ on Stack Overflow

How to update javascript object

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related