Javascript notation for objects was thought to be so concise and good that it started to be used outside of the language, just for data, and became called JavaScript Object Notation (or JSON).

The web started with languages close to HTML, like XML and derivatives, but JSON ended up winning because of its simplicity.

This standardized notation uses the object notation in its simplest form. A JSON value can be:

• strings (double quoted),
• numbers (both integer and real),
• booleans (true and false),
• null, and
• objects: delimited with {} with fields being double quoted, always. Values of fields can be any valid JSON value.
• arrays: delimited with [] with JSON values inside.

One particular difference with modern notation in Javascript is the comma after the last element in an array or object: it is allowed in modern Javascript but not in JSON. Another annoyance is

[
  "first",
  2,
  {
    "x": 0.5,
    "y": null
  },
  [true, true, true]
]

The comma after the null (field "y") is wrong, and so is the comma after the array of 3 true values (and there cannot be a comment besides it because JSON doesn't allow comments!).

Encoding and Decoding

To parse JSON in Javascript the function JSON.parse receives a string and recreates a Javascript object which contains the same data.

const obj = JSON.parse(`{"first":"James","age":27}`);

To produce JSON from in-memory objects, JSON.stringify receives an arbitrary Javascript object and converts it to a string encoding that object in JSON:

const obj = { first: 'James', age: 27 };
console.log(JSON.stringify(obj));