JS: JSON.parse

JSON.parse(json_string)

Convert JSON string to a JavaScript value.

console.log(
JSON.parse('{"a":3 , "b":[4,2]}')
);

// prints { a: 3, b: [ 4, 2 ] }

JSON.parse takes optional 2nd arg. For detail, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse

Reference

ECMAScript 2015 §Structured Data#sec-json.parse