how to unstringify array of objects not JSON in javascript code example

Example 1: javascript parse json

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

Example 2: 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