JSON Serialization in JavaScript, Python, and Other Languages

jsonserializationjavascriptpython

JSON serialization converts objects to JSON strings, and deserialization converts them back. Every language handles this differently.

JavaScript / TypeScript

// Serialize


const json = JSON.stringify({ name: "Alice", age: 30 }, null, 2);
// Deserialize


const obj = JSON.parse(json);
// Custom serialization with replacer


const json2 = JSON.stringify(obj, (key, value) => {


  if (value instanceof Date) return value.toISOString();


  return value;


});
// Reviver for deserialization


const obj2 = JSON.parse(json2, (key, value) => {


  if (key.endsWith('Date')) return new Date(value);


  return value;


});

Limitations: No support for undefined, functions, Dates, Map, Set, or circular references.

Python

import json


from datetime import datetime
# Serialize


data = {"name": "Alice", "age": 30}


json_str = json.dumps(data, indent=2)
# Deserialize


obj = json.loads(json_str)
# Custom encoder for dates


class DateEncoder(json.JSONEncoder):


    def default(self, obj):


        if isinstance(obj, datetime):


            return obj.isoformat()


        return super().default(obj)
json_str = json.dumps({"created": datetime.now()}, cls=DateEncoder)

Go

import "encoding/json"
type User struct {


    Name string json:"name"


    Age  int    json:"age"


}
// Serialize


user := User{Name: "Alice", Age: 30}


bytes, _ := json.Marshal(user)
// Deserialize


var result User


json.Unmarshal(bytes, &result)

Java

import com.fasterxml.jackson.databind.ObjectMapper;
ObjectMapper mapper = new ObjectMapper();
// Serialize


String json = mapper.writeValueAsString(user);
// Deserialize


User user = mapper.readValue(json, User.class);

Common Pitfalls

  • Date handling — JSON has no Date type; use ISO 8601 strings

  • BigInt — JavaScript JSON.stringify loses precision for large numbers

  • Circular references — Will throw TypeError; use libraries like flatted

  • Enum values — Handle explicitly in each language

    • Format your serialized output with our JSON Formatter for readability.

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