When receiving json data from a web server, it´s a string.
Convert it to a javascript object with JSON.parse()
const jsonFromWeb = '{"name": "John", "age": 30}'
const obj = JSON.parse(jsonFromWeb);
obj.name
obj["age"]
Note: Also work with array
When sending data to a web server, the data has to be a string.
Convert a javascript object to a string with JSON.stringify()
const obj = '{"name": "John", "age": 30}'
const str = JSON.stringify(obj);
// send it
Note: Also work with array