Stringify (convert to JSON) a JavaScript object with circular reference

Circular structure error occurs when you have a property of the object which is the object itself directly (a -> a) or indirectly (a -> b -> a).

To avoid the error message, tell JSON.stringify what to do when it encounters a circular reference.
For example, if you have a person pointing to another person (“parent”), which may (or may not) point to the original person, do the following:

JSON.stringify( that.person, function( key, value) {
  if( key == 'parent') { return value.id;}
  else {return value;}
})

The second parameter to stringify is a filter function. Here it simply converts the referred object to its ID, but you are free to do whatever you like to break the circular reference.

You can test the above code with the following:

function Person( params) {
  this.id = params['id'];
  this.name = params['name']; 
  this.father = null;
  this.fingers = [];
  // etc.
}

var me = new Person({ id: 1, name: 'Luke'});
var him = new Person( { id:2, name: 'Darth Vader'});
me.father = him; 
JSON.stringify(me); // so far so good

him.father = me; // time travel assumed :-)
JSON.stringify(me); // "TypeError: Converting circular structure to JSON"
// But this should do the job:
JSON.stringify(me, function( key, value) {
  if(key == 'father') { 
    return value.id;
  } else {
    return value;
  };
});

BTW, I’d choose a different attribute name to “parent” since it is a reserved word in many languages (and in DOM). This tends to cause confusion down the road…