Do JSON.stringify() and JSON.parse() change data type?

Question

👋 I need a little bit of help to understand JSON better.

When I stringify an array with class objects then parse it back, it looks like the array loses the class instance. Can I keep the class even after parse JSON data, and if can, how? And why does this happen?

Here is the code:

class Account {
    constructor(site, login, pass) {
        this.site = site,
        this.login = login
        this.pass = pass
    }
}
const accounts = [
    new Account("website1.com", "[email protected]", "12345"),
    new Account("website2.com", "[email protected]", "23456")
]
console.log('BEFORE', accounts)


const string = JSON.stringify(accounts)
console.log(string)


const parseString = JSON.parse(string)
console.log('AFTER', parseString)

The console shows like this:

BEFORE (2) [Account, Account]
{string: "[{"site":"website1.com","login":"[email protected]"….com","login":"[email protected]","pass":"23456"}]"}
AFTER (2) [{…}, {…}]

To make things clear, is it possible to have [Account, Account] after JSON.parse()`?

Let me know if my explanation is not clear. Thank you so much!

Answer 1

JSON has no support for types other than object, array, null, string, number and boolean.

If you kind of know what you can expect in your JSON, you can use a reviver function during parsing. For your example, this suffices:

JSON.parse(string, (k, v) => v.hasOwnProperty('site')
                             ? new Account(v.site, v.login, v.pass)
                             : v);