Example of a circular reference in Javascript?

Question

I was wondering if anyone has a good, working example of a circular reference in javascript? I know this is incredibly easy to do with closures, but have had a hard time wr

Answer 1

window.onload = function() {
  hookup(document.getElementById('menu'));

  function hookup(elem) {
    elem.attachEvent( "onmouseover", mouse);

    function mouse() {
    }
  }
}

As you can see, the handler is nested within the attacher, which means it is closed over the scope of the caller.

Answer 2

Or even simpler, an array "containing" itself. See example:

var arr = [];
arr[0] = arr;

Answer 3

You can do:

• window.window...window
• var circle = {}; circle.circle = circle;
• var circle = []; circle[0] = circle; or circle.push(circle)
• function Circle(){this.self = this}; var circle = new Circle()

Answer 4

Probably the shortest way to define a cyclic object.

a = {}; a.a = a;

Answer 5

var b = [];
var a = [];
a[0] = b;
b[0] = a;

Printing a or b would return Circular.

Answer 6

A simple way to create a circular reference is to have an object that refers to itself in a property:

function Foo() {
  this.abc = "Hello";
  this.circular = this;
}

var foo = new Foo();
alert(foo.circular.circular.circular.circular.circular.abc);

Here the foo object contains a reference to itself.

With closures this is usually more implicit, by just having the circular reference in scope, not as an explicit property of some object:

var circular;

circular = function(arg) {
  if (arg) {
    alert(arg);
  }
  else {
    // refers to the |circular| variable, and by that to itself.
    circular("No argument");
  }
}

circular("hello");
circular();

Here the function saved in circular refers to the circular variable, and thereby to itself. It implicitly holds a reference to itself, creating a circular reference. Even if circular now goes out of scope, it is still referenced from the functions scope. Simple garbage collectors won't recognize this loop and won't collect the function.