How to detect circular structures?

For example, this code:

var a = {};
a.a = a;
JSON.stringify(a);

Will throw:

TypeError: Converting circular structure to JSON

My question is, how to detect a circular structure?

Crockford's JSON implementation does just that. It looks like it just keeps a list while traversing the object graph. The code is fairly easy to follow.

Here is function using native JSON detection

function isCircular (d) {
  try {JSON.stringify(d)}
  catch (e) {return true}
  return false
}