JSON (JavaScript Object Notation) is a lightweight data format that has become the standard for data interchange on the web. JSON can represent either lists of values (arrays) or collections of name/value pairs (objects). JavaScript provides methods to encode objects/arrays to JSON strings (JSON.stringify) and decode JSON strings back to objects/arrays (JSON.parse). For a data structure to be valid JSON, it must follow certain formatting rules like using double quotes for object property names and only allowing specific data types like strings, numbers, booleans, objects, arrays, and null.

1. Unit-2
Working with JSON

2. What is JSON?
J ava S cript O bject N otation, or JSON, is a lightweight data format
that has become the defacto standard for the web. JSON can be
represented as either a list of values, e.g. an Array, or a hash of
properties and values, e.g. an Object.
Array, Object
[ a, m, y ]
{ name : value }

3. // a JSON array
["one", "two", "three"]
// a JSON object
{
"one": 1, // name : “Mukesh”
"two": 2,
"three": 3
}
Format of Node.js Object: JSON-
object
• Create an Object of student:
var student =
{
Name: "Amit",
Branch:"BCA",
City: "kathmandu",
Mobile: "99946730"
};

4. Encoding and Decoding
JavaScript provides 2 methods for encoding data structures to json and
encoding json back to JavaScript objects and arrays. They are both
available on the JSON object that is available in the global scope.
JSON.stringify takes a JavaScript object or array and returns a serialized
string in the JSON format.

5. const data = {
name: 'John Doe',
age: 32,
title: 'Vice President of JavaScript'
};
const jsonStr = JSON.stringify(data);
console.log(jsonStr);
// prints '{"name":"John Doe","age":32,"title":"Vice President of
JavaScript"}'

6. JSON.parse takes a JSON string and decodes it to a
JavaScript data structure.
const jsonStr =
'{"name":"John Doe","age":32,"title":"Vice President of JavaScript"}';
const data = JSON.parse(jsonStr);
console.log(data.title);
// prints 'Vice President of JavaScript'

7. What is valid JSON?
There are a few rules to remember when dealing with data in JSON
format. There are several gotchas that can produce invalid JSON as well.
• Empty objects and arrays are okay
• Strings can contain any unicode character, this includes object properties
• null is a valid JSON value on it's own
• All object properties should always be double quoted
• Object property values must be one of the following: String, Number,
Boolean, Object, Array, null
• Number values must be in decimal format, no octal or hex
representations
• Trailing commas on arrays are not allowed

8. These are all examples of valid JSON.
{"name":"John Doe","age":32,"title":"Vice President of JavaScript"}
["one", "two", "three"]
// nesting valid values is okay
{"names": ["John Doe", "Jane Doe"] }
[ { "name": "John Doe"}, {"name": "Jane Doe"} ]
{} // empty hash
[] // empty list
null
{ "key": "uFDD0" } // unicode escape codes

9. These are all examples of bad JSON formatting.
{ name: "John Doe", 'age': 32 } // name and age should be in double
quotes
[32, 64, 128, 0xFFF] // hex numbers are not allowed
{ "name": "John Doe", "age": undefined } // undefined is an invalid
value
// functions and dates are not allowed
{ "name": "John Doe",
"birthday": new Date('Fri, 26 Jan 2019 07:13:10 GMT'),
"getName": function() {
return this.name;
}}

10. Calling JSON.parse with an invalid JSON string will result in a
SyntaxError being thrown. If you are not sure of the validity of your
JSON data, you can anticipate errors by wrapping the call in a try/catch
block.
Notice that the only complex values allowed in JSON are objects and
arrays. Functions, dates and other types are excluded. This may not
seem to make sense at first. But remember that JSON is a data format,
not a format for transferring complex JavaScript objects along with their
functionality.

11. Example-1
const book = {
title : “Node.js Book",
author : "Basarat Ali Syed"
}
const bookJSON = JSON.stringify(book)
console.log(book)
console.log(bookJSON)

12. Example-2
const book =
{
title : "Narinder Modi",
author : "xyz"
}
const bookJSON = JSON.stringify(book)
console.log(book.title)
console.log(bookJSON.title)

13. Example-3
const book =
{
title : "Narinder Modi",
author : "xyz"
}
const bookJSON = JSON.stringify(book)
console.log(book.title)
console.log(bookJSON.title)
const bookObj = JSON.parse(bookJSON)
console.log(bookObj.title)

14. Example-4
const fs = require("fs")
const book = {
title : "Narinder Modi",
author : "xyz"
}
const bookJSON = JSON.stringify(book)
console.log(book.title)
console.log(bookJSON.title)
const bookObj = JSON.parse(bookJSON)
console.log(bookObj.title)
fs.writeFileSync("myjson.json",bookJSON)

15. Example-5
const fs = require("fs")
//const book = {
// title : "Narinder Modi",
// author : "xyz"
//}
//const bookJSON = JSON.stringify(book)
//console.log(book.title)
//console.log(bookJSON.title)
//const bookObj = JSON.parse(bookJSON)
const dataBuffer = fs.readFileSync("myjson.json")
//console.log(dataBuffer)
console.log(dataBuffer.toString())

16. Example-6
const fs = require("fs")
//const book = {
// title : "Narinder Modi",
// author : "xyz"
//}
//const bookJSON = JSON.stringify(book)
//console.log(book.title)
//console.log(bookJSON.title)
//const bookObj = JSON.parse(bookJSON)
const dataBuffer = fs.readFileSync("myjson.json")
//console.log(dataBuffer)
const dataJSON = dataBuffer.toString()
const bookObj = JSON.parse(dataJSON)
console.log(bookObj)

17. Example-7
const fs = require("fs")
//const book = {
// title : "Narinder Modi",
// author : "xyz"
//}
//const bookJSON = JSON.stringify(book)
//console.log(book.title)
//console.log(bookJSON.title)
//const bookObj = JSON.parse(bookJSON)
const dataBuffer = fs.readFileSync("myjson.json")
//console.log(dataBuffer)
const dataJSON = dataBuffer.toString()
const bookObj = JSON.parse(dataJSON)
console.log(bookObj.title)