JSON (JavaScript Object Notation)

• A lightweight, plain-text format used to represent structured data. It is easy for humans to read and write, and easy for machines to parse and generate.
• JSON is widely used for transmitting data between a server and a web application as it is language-independent and can be parsed by many programming languages.
• Using the native JavaScript JSON object, you can easily convert JSON to a JavaScript object and vice versa.

Converting JSON to an Object

let jsonString = '{"students":[{"id":1,"name":"Alice"},{"id":2,"name":"Bob"},{"id":3,"name":"Charlie"}]}';
 
// Convert to an Object:
let obj = JSON.parse(jsonString);
 
// Access the 2nd student (Bob)
console.log(obj.students[1].name); // Bob

• JSON.parse(jsonString): Converts the JSON string into a JavaScript object.
• obj.students[1].name: Accesses the name of the second student in the array.

Converting an Object to JSON

let obj = {
  students: [
    { id: 1, name: 'Alice' },
    { id: 2, name: 'Bob' },
    { id: 3, name: 'Charlie' },
  ],
};
 
let jsonString = JSON.stringify(obj);
 
console.log(jsonString); // Outputs: '{"students":[{"id":1,"name":"Alice"},{"id":2,"name":"Bob"},{"id":3,"name":"Charlie"}]}'

• JSON.stringify(obj): Converts the JavaScript object into a JSON string.
• jsonString: The resulting JSON string representing the object.

Caveats When Using JSON

• JSON works well for converting objects to a string (serialization) and back to an object (deserialization). However, some data types do not convert well.
• JSON only supports primitive data types (string, number, boolean, null) and arrays/objects. It does not support functions, dates, or undefined values.

Object Instances

Instances of objects in memory, such as Date objects, lose their methods when converted to JSON.

let event = {
  title: 'Meeting',
  date: new Date('2023-06-15T14:00:00Z'),
};
 
console.log(event.date.toISOString()); // 2023-06-15T14:00:00.000Z
 
// Convert to JSON
let jsonEvent = JSON.stringify(event);
 
// Restore (convert to object)
let eventFromJSON = JSON.parse(jsonEvent);
 
console.log(eventFromJSON.date); // "2023-06-15T14:00:00.000Z"

• During conversion to JSON, the Date object is converted to a string.
• Methods on the Date object are lost, so eventFromJSON.date is just a string, not a Date object.

Functions (Methods)

Functions (methods) in objects are not included in the JSON representation.

let counter = {
  count: 0,
  increment: function () {
    this.count++;
  },
};
 
console.log(counter.count); // 0
counter.increment();
console.log(counter.count); // 1
 
// Convert to JSON
let jsonCounter = JSON.stringify(counter);
 
// Restore (convert to object)
let counterFromJSON = JSON.parse(jsonCounter);
 
console.log(counterFromJSON.count); // 0
counterFromJSON.increment(); // TypeError: counterFromJSON.increment is not a function

• During conversion to JSON, the increment function is not included.
• The resulting object from JSON does not have the increment method.