jquery extend vs angular extend

Javascript Problem Overview

What is the difference between these two extend functions?

  angular.extend(a,b);
  $.extend(a,b);

While the jquery.extend is well documented the angular.extend lacks details and the comments there provide no answers. (https://docs.angularjs.org/api/ng/function/angular.extend).

Does angular.extend also provide deep copy?

Javascript Solutions

Solution 1 - Javascript

angular.extend and jQuery.extend are very similar. They both do a shallow property copy from one or more source objects to a destination object. So for instance:

var src = {foo: "bar", baz: {}};
var dst = {};
whatever.extend(dst, src);
console.log(dst.foo);             // "bar"
console.log(dst.baz === src.baz); // "true", it's a shallow copy, both
                                  // point to same object

angular.copy provides a deep copy:

var src = {foo: "bar", baz: {}};
var dst = angular.copy(src);
console.log(dst.baz === src.baz); // "false", it's a deep copy, they point
                                  // to different objects.

Getting back to extend: I only see one significant difference, which is that jQuery's extend allows you to specify just one object, in which case jQuery itself is the target.

Things in common:

It's a shallow copy. So if src has a property p that refers to an object, dst will get a property p that refers to the same object (not a copy of the object).
They both return the destination object.
They both support multiple source objects.
They both do the multiple source objects in order, and so the last source object will "win" in case more than one source object has the same property name.

Test page: Live Copy | Live Source

<!DOCTYPE html>
<html>
<head>
<script src="http://code.jquery.com/jquery-1.9.1.min.js"></script>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.0.5/angular.min.js"></script>
<meta charset=utf-8 />
<title>Extend!</title>
</head>
<body>
  <script>
    (function() {
      "use strict";
      var src1, src2, dst, rv;
      
      src1 = {
        a: "I'm a in src1",
        b: {name: "I'm the name property in b"},
        c: "I'm c in src1"
      };
      src2 = {
        c: "I'm c in src2"
      };
      
      // Shallow copy test
      dst = {};
      angular.extend(dst, src1);
      display("angular shallow copy? " + (dst.b === src1.b));
      dst = {};
      jQuery.extend(dst, src1);
      display("jQuery shallow copy? " + (dst.b === src1.b));
      $("<hr>").appendTo(document.body);

      // Return value test
      dst = {};
      rv = angular.extend(dst, src1);
      display("angular returns dst? " + (rv === dst));
      dst = {};
      rv = jQuery.extend(dst, src1);
      display("jQuery returns dst? " + (rv === dst));
      $("<hr>").appendTo(document.body);

      // Multiple source test
      dst = {};
      rv = angular.extend(dst, src1, src2);
      display("angular does multiple in order? " +
                  (dst.c === src2.c));
      dst = {};
      rv = jQuery.extend(dst, src1, src2);
      display("jQuery does multiple in order? " +
                  (dst.c === src2.c));
      
      function display(msg) {
        $("<p>").html(String(msg)).appendTo(document.body);
      }
    })();
  </script>
</body>
</html>

Solution 2 - Javascript

There is one subtle difference between the two which was not mentioned in previous answers.

jQuery's .extend() allows you to conditionally add key,value pairs, only if the value is defined. So in jQuery, this: $.extend({}, {'a': x ? x : undefined}); will return {} in case x is undefined.

In Angular's .extend() however, this: angular.extend({}, {'a': x ? x : undefined}); will return {'a': undefined}, even if x is undefined. So the key will be there, no matter what.

This could be a good or a bad thing, depending on what you need. Anyway this is a difference in behavior between the two libraries.

Solution 3 - Javascript

The 1.0.7 angularjs build states that the extend & copy methods no longer copy over the angularjs internal $$hashKey values.

See release notes @ https://github.com/angular/angular.js/blob/master/CHANGELOG.md

angular.copy/angular.extend: do not copy $$hashKey in copy/extend functions. (6d0b325f, #1875)

A quick test of the angular.copy in Chomre dev tools method shows that it does do a deep copy.

x = {p: 3, y: {x: 5}}
Object {p: 3, y: Object}
x
Object {p: 3, y: Object}
z = angular.copy(x);
Object {p: 3, y: Object}
z
Object {p: 3, y: Object}
x
Object {p: 3, y: Object}
z.y.x = 1000
    1000
x
Object {p: 3, y: Object}
p: 3
y: Object
    x: 5
    __proto__: Object
__proto__: Object
z
Object {p: 3, y: Object}
p: 3
y: Object
   x: 1000
   __proto__: Object
__proto__: Object

angular.extend on the other hand does a shallow copy.

Solution 4 - Javascript

.extend() in AngularJS works similarly to jQuery's .extend()

http://jsfiddle.net/Troop4Christ/sR3Nj/

var o1 = {
    a: 1,
    b: 2,
    c: {
        d:3,
        e:4
    }
},
    o2 = {
        b: {
            f:{
                g:5
            }
        }
    };


console.log(angular.extend({}, o1, o2));
console.log(o1);
console.log(o2);

Content Type	Original Author	Original Content on Stackoverflow
Question	Renaud	View Question on Stackoverflow
Solution 1 - Javascript	T.J. Crowder	View Answer on Stackoverflow
Solution 2 - Javascript	asafge	View Answer on Stackoverflow
Solution 3 - Javascript	Mike Pugh	View Answer on Stackoverflow
Solution 4 - Javascript	RavenHursT	View Answer on Stackoverflow