What is it

Language independent, lightweight data storing

{
  "first_name": "John",
  "last_name": "Smith",
  "is_alive": true,
  "age": 27,
  "address": {
    "street_address": "21 2nd Street",
    "city": "New York",
    "state": "NY",
    "postal_code": "10021-3100"
  },
  "phone_numbers": [
    {
      "type": "home",
      "number": "212 555-1234"
    },
    {
      "type": "office",
      "number": "646 555-4567"
    }
  ],
  "children": [
    "Catherine",
    "Thomas",
    "Trevor"
  ],
  "spouse": null
}

JSON.parse()

JSON.parse() method parses a JSON string, constructing the JavaScript value or object described by the string

const json = '{"result":true, "count":42}';
const obj = JSON.parse(json);

console.log(obj.count); // 42
console.log(obj.result); // true

Caveats

Single vs Double Quotes

JSON object should use single quotes '' to wrap records as a string

• should be using double quotes "" for key
• should NOT be using double quotes for wrapping the JSON records

// WRONG: will throw a SyntaxError
JSON.parse("{'foo': 1}");

parse does not allow trailing commas or empty records

// WRONG: both will throw a SyntaxError
JSON.parse('[1, 2, 3, 4, ]');
JSON.parse('{"foo" : 1, }');

JSON.stringify()

Converts JS object or value to a JSON string

JSON.stringify({ x: 5, y: 6 }); // "{"x":5,"y":6}"
JSON.stringify({}) // '{}' 
JSON.stringify(true) // 'true' 
JSON.stringify('foo') // '"foo"' 
JSON.stringify([1, 'false', false]) // '[1,"false",false]' 
JSON.stringify([NaN, null, Infinity]) // '[null,null,null]' 
JSON.stringify({ x: 5 }) // '{"x":5}'
JSON.stringify(new Date(2006, 0, 2, 15, 4, 5)) // '"2006-01-02T15:04:05.000Z"'

Can stringify array of objects

JSON.stringify(
  [
    new Number(3), 
    new String('false'), 
    new Boolean(false)
  ]
); // "[3,"false",false]"

Some data types will be forced to null when stringified

JSON.stringify(
  {
    x: [10, undefined, function(){}, Symbol('')] 
  }
); // "{"x":[10,null,null,null]}"