JSON.stringify & JSON.parse

In JavaScript, JSON.stringify and JSON.parse are two essential methods used to convert data between JavaScript objects and JSON strings. Understanding these methods is key to handling data interchange, especially when working with APIs or storing data.

JSON.stringify

JSON.stringify converts a JavaScript object or value to a JSON-formatted string.

• Useful for sending data to a server or saving it as text
• Can accept additional arguments for filtering or formatting

const user = { name: "Alice", age: 25, active: true };
const jsonString = JSON.stringify(user);
console.log(jsonString);

JSON.parse

JSON.parse converts a JSON-formatted string back into a JavaScript object or value.

• Used when receiving JSON data as text (e.g., from an API)
• Throws an error if the string is not valid JSON

const jsonString = '{"name":"Alice","age":25,"active":true}';
const user = JSON.parse(jsonString);
console.log(user.name);  // Output: Alice

Additional Tips

• JSON.stringify ignores functions, symbols, and undefined values.
• Dates are serialized as ISO strings by JSON.stringify.
• You can provide a replacer function or array to JSON.stringify to customize serialization.
• JSON.parse accepts an optional reviver function to transform parsed values.

// Replacer example: exclude 'age' property
const user = { name: "Bob", age: 30, active: false };
const jsonString = JSON.stringify(user, ['name', 'active']);
console.log(jsonString);  // {"name":"Bob","active":false}

// Reviver example: convert date string back to Date object
const jsonDate = '{"event":"meeting","date":"2024-06-01T10:00:00.000Z"}';
const obj = JSON.parse(jsonDate, (key, value) => {
  if (key === 'date') return new Date(value);
  return value;
});
console.log(obj.date instanceof Date);  // true