What are the specific properties skipped by stringify

Some of JavaScript-specific object properties are skipped by JSON.stringify.

What are those ?

1. Function properties - means methods
2. Symbolic properties.
3. Properties that store undefined.

let user = {
  sayHi() { // ignored
    alert("Hello World");
  },
  [Symbol("id")]: 123, // ignored
  something: undefined // ignored
};

alert( JSON.stringify(user) ); // {} (empty object)

However, another good here is, nested objects are supported and converted automatically.

let testNestedObjects = {
  title: "NestedCheck",
  test1: {
    number: 123,
    participants: ["test25", "test26"]
  }
};

alert( JSON.stringify(testNestedObjects) );

Output:

{
  "title":"NestedCheck",
  "test1":{"number":123,"participants":["test25","test26"]},
}