console.log(JSON.parse('{"data":"{"json":"rocks"}"}'));

print_r(json_decode('{"data":"{"json":"rocks"}"}', true));

{"data":"{"json":"rocks"}"}

'{"data":"{\"json\":\"rocks\"}"}'

console.log(JSON.parse('{"data":"{\"json\":\"rocks\"}"}'));

console.log(JSON.parse('{"data":"{\"json\":\"rocks\"}"}'));​

console.log(JSON.parse('{"data":{"json":"rocks"}}'));