js string to object

var mystr = '{ "hello":"world" }' // NB: Has enclosing ""
var myobj = JSON.parse(mystr);

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

Use the JavaScript function JSON.parse() to convert text into a JavaScript object:
var obj = JSON.parse('{ "name":"John", "age":30, "city":"New York"}');

const json = '{ "fruit": "pineapple", "fingers": 10 }';
const obj = JSON.parse(json);
console.log(obj.fruit, obj.fingers);

JSON.parse()

str = "firstName:name1, lastName:last1"; // NB: No enclosing ""
obj = eval('({' + str + '})');