How to Stringify function

What will be the output

var obj = { "name":"John", "age":function () {return 30;}, "city":"New York"};
var myJSON = JSON.stringify(obj);
document.getElementById("demo").innerHTML = myJSON;

Ans:

{"name":"John","city":"New York"}

How to print function

var obj = { "name":"John", "age":function () {return 30;}, "city":"New York"};
obj.age = obj.age.toString();
var myJSON = JSON.stringify(obj);
document.getElementById("demo").innerHTML = myJSON;