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JSON

📖 Deeper dive reading:

JavaScript Object Notation (JSON) was conceived by Douglas Crockford in 2001 while working at Yahoo! JSON, pronounced like the name Jason, received official standardization in 2013 and 2017 (ECMA-404, RFC 8259).

JSON provides a simple, and yet effective way, to share and store data. By design JSON is easily convertible to, and from, JavaScript objects. This makes it a very convenient data format when working with web technologies. Because of its simplicity, standardization, and compatibility with JavaScript, JSON has become one of the world's most popular data formats.

Format

A JSON document contains one of the following data types:

Type Example
string "crockford"
number 42
boolean true
array [null,42,"crockford"]
object {"a":1,"b":"crockford"}
null null

Most commonly, a JSON document contains an object. Objects contain zero or more key value pairs. The key is always a string, and the value must be one of the valid JSON data types. Key value pairs are delimited with commas. Curly braces delimit an object, square brackets and commas delimit arrays, and strings are always delimited with double quotes.

Here is an example of a JSON document.

{
  "class": {
    "title": "web programming",
    "description": "Amazing"
  },
  "enrollment": ["Marco", "Jana", "فَاطِمَة"],
  "start": "2025-02-01",
  "end": null
}

JSON is always encoded with UTF-8. This allows for the representation of global data.

Converting to JavaScript

You can convert JSON to, and from, JavaScript using the JSON.parse and JSON.stringify functions.

const obj = { a: 2, b: 'crockford', c: undefined };
const json = JSON.stringify(obj);
const objFromJson = JSON.parse(json);

console.log(obj, json, objFromJson);

// OUTPUT:
// {a: 2, b: 'crockford', c: undefined}
// {"a":2, "b":"crockford"}
// {a: 2, b: 'crockford'}

Note that in this example, JSON cannot represent the JavaScript undefined object and so it gets dropped when converting from JavaScript to JSON.