Rose Perrone Rose Perrone - 4 months ago 15
jQuery Question

jquery.extend(true, [], obj) not creating a deep copy

jsFiddle here.

If deep copying worked, the output would be "Curious George" and not "Ender's Game". How can I make a deep copy? An answer to this question indicates that

$.extend(true, [], obj)
creates a deep copy. Yet my example shows that it doesn't.

function Person(){}
Person.prototype.favorite_books = [];

var george = new Person();
george.favorite_books = ["Curious George"];

var kate = new Person();
kate.favorite_books = ["The Da Vinci Code", "Harry Potter"];

var people = [kate, george];

var people_copy = $.extend(true, [], people);
people_copy[0].favorite_books[0] = "Ender's Game";

$('#text').text(people[0].favorite_books[0]);


SOLUTION

I updated the jsFiddle. It turns out I need to deep copy each object in the array individually if the object is a custom object (that is,
$.isPlainObject
returns false).

Answer

And now here is the real answer:

At the moment jQuery can only clone plain JavaScript Objects, while you're using custom ones. And that's obvious, since jQuery cannot know how exactly to instantiate a new custom object. So this works as expected:

var george = {};
george.favorite_books = ["Curious George"];

var kate = {};
kate.favorite_books = ["The Da Vinci Code", "Harry Potter"];

var people = [kate, george];

var people_copy = $.extend(true, [], people);

console.log(people_copy[0].favorite_books == people[0].favorite_books);

Reference to a jQuery code: https://github.com/jquery/jquery/blob/master/src/core.js#L305

See that it checks if it's jQuery.isPlainObject(copy) or it's an array. Otherwise it performs just a reference copy.