Most of the time,

JSON.stringify

is used with the first argument only. But if we need to fine-tune the replacement process, like to filter out

circular references

, we can use the second argument of

JSON.stringify

let room = {
  number: 23
};

let meetup = {
  title: "Conference",
  participants: [{name: "John"}, {name: "Alice"}],
  place: room // meetup references room
};

room.occupiedBy = meetup; // room references meetup

document.write( JSON.stringify(meetup, ['title', 'participants']) );

If we pass an array of properties to it, only these properties will be encoded, so the result will be:

{"title":"Conference","participants":[{},{}]}

As the result shows, the property list is applied to the whole object structure. So the objects in

participants

are empty, because

name

is not in the list. Let’s include in the list every property except

room.occupiedBy

that would cause the circular reference:

let room = {
  number: 23
};

let meetup = {
  title: "Conference",
  participants: [{name: "John"}, {name: "Alice"}],
  place: room // meetup references room
};

room.occupiedBy = meetup; // room references meetup

document.write( JSON.stringify(meetup, ['title', 'participants', 'place', 'name', 'number']) );

The result will be:

{"title":"Conference","participants":[{"name":"John"},{"name":"Alice"}],"place":{"number":23}}

Now everything except

occupiedBy

is serialized. But the list of properties is quite long. Fortunately, we can use a function instead of an array as the

replacer

.