how to json parse a function from a string code example

Example 1: Javascript object to JSON string

var person={"first_name":"Tony","last_name":"Hawk","age":31};
var personJSONString=JSON.stringify(person);

Example 2: javascript parse json

var jsonPerson = '{"first_name":"billy", "age":23}';
var personObject = JSON.parse(jsonPerson); //parse json string into JS object

Example 3: json parse returns object

var str = '[{"UserName":"xxx","Rolename":"yyy"}]'; // your response in a string
    var parsed = JSON.parse(str); // an *array* that contains the user
    var user = parsed[0];         // a simple user
    console.log(user.UserName);   // you'll get xxx
    console.log(user.Rolename);   // you'll get yyy