Circular reference in value argument not supported
An attempt has been made to invoke JSON.stringify with a value that is not valid. The value argument, an array or object, contains a circular reference.
To correct this error
Remove the circular reference from the argument.
The code in this example causes a runtime error because john has a reference to mary and mary has a reference to john. to remove the circular reference, either remove or unset the property brother from the mary object or the sister property from the john object.