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 wrapping my brain around this. An example that I can dissect in Firebug would be most appreciated.

Thanks

Answer 1

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.