Javascript object reference linked to object in array?

Question

If I have an object:

var array = [];
var theobject = null;

array.push({song:"The Song", artist:"The Artist"}, {song:"Another Song", artist:"Another Artist"});

and I do:

for(var i = 0; i < array.length; i++)
if(array[i].song == "The Song") {
theobject = array[i];
break;
}

If I then change theobject by doing:

theobject.song = "Changed Name";

I am having problems where despite myself trying to set ONLY "theobject.song" to be equal to "Changed Name", array[0].song becomes set to "Changed Name" also.

What I want is "theobject.song" to become "Changed Name" while array[0].song remains "The Song".

What is the best way to accomplish this?

Why don't you just try it out

blockhead
– blockhead

2012-05-09 04:58:14 +00:00
Commented May 9, 2012 at 4:58 — blockhead
– blockhead, Commented May 9, 2012 at 4:58

KooiInc · Accepted Answer · 2012-05-09 05:48:15Z

9

You will never get a reference to your object in the loop. Try:

for(var i = 0; i < array.length; i++)
 if(array[i].song === "The Song") {
 theobject = array[i];
 break;
}

That will give a reference to the object, and you will be able to change the objects song property.

If you want to use a copy of the object, then you'll have to do a manual copy. E.g.

function clone(obj) {
  var copy = {};
  for (var attr in obj) {
   if (obj.hasOwnProperty(attr)) {
     copy[attr] = obj[attr];
   }
  }
  return copy;
}

And your loop becomes:

for(var i = 0; i < array.length; i++)
 if(array[i].song === "The Song") {
 theobject = clone(array[i]);
 break;
}

edited May 9, 2012 at 5:48

answered May 9, 2012 at 5:01

KooiInc

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1 Comment

Rolando Over a year ago

I do not want the refrence, I want a copy. I want to change the song property of only theobject, not the original array.

Tarik Chakur · Accepted Answer · 2017-06-10 16:08:06Z

1

It possible to use Object.assign() to only copy its value without the reference.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign

var array = [];
var theobject = null;

array.push({
  song:"The Song", 
  artist:"The Artist"
  }, 
  {
  song:"Another Song", 
  artist:"Another Artist"
});

for(var i = 0; i < array.length; i++)
  if(array[i].song == "The Song") {
    theobject = Object.assign( {}, array[i] );
    break;
  }
  
theobject.song = "Changed Name";

console.log( array );
console.log( theobject );

answered Jun 10, 2017 at 16:08

Tarik Chakur

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