JSON File Format

JSON is a way to store data. A visually readable format. JSON stands for JavaScript Object Notation.

JSON is a file format, but it is also used for arrays and dictionaries in the JavaScript programming language. So you could copy the full contents of your JSON file into a variable in javascript without any problems.

Other programming languages also support formats like JSON, but it’s most of the time not actual JSON, take for example php, it does function alike, but the design is different.

JSON can store strings, intagers, floats, booleans, null’s and the pointer type variables: arrays and dictionaries.

Syntax

In this section I’ll show what the structure looks like.

In JSON you always have atleast 1 [] or {}. This is the top level List or Dict.

A dictionary in JSON can only have strings as keys. In JavaScript you can have intagers and probably other types as keys, but they will be turned into strings internally.

Here is an example of a dictionary in JSON:

{
   "string": "ello",
   "int": 7,
   "bool1": true,
   "bool2": false,
   "float": 3.14,
   "null": null,
   "array": [],
   "dictionary": {}
}

Here I have listed all things the JSON format accepts inside a dictionary value. In some parsers you can put down comments, but that is not accepted in normal plain JSON.

Here is what an array looks like:

[
  "owo",
  1,
  3.14,
  false,
  true,
  null,
  [],
  {}
]

Whenever you put an array or dictionary inside another array or dictionary it’s called a nested dictionary/array.

Nesting Limit

There is no theoretical limit to how deep JSON objects can be nested, but there usually is a practical limit based on the decoder being used. For example, PHP’s json_decode() has a default limit of 512 levels. _source

JavaScript things

The only reason that I cover this is because JSON originates from JS.

In JavaScript you can simply turn JSON into a string and vice versa. This is needed for sending it over internet protocols like MQTT for example. Here is how to do it:

const obj = JSON.parse('{"name":"John", "age":30, "city":"New York"}');
 
const obj = {name: "John", age: 30, city: "New York"};
const myJSON = JSON.stringify(obj);

JavaScript can also have more types as values inside the JSON structure. In JavaScript you can have functions, enums, undefined and objects. this means you can have more advanced data structures. When you try to stringify these, the functions will be stripped, and so will they from the objects, but the fields will be turned into a dictionary. undefined will be removed, and enums will be converted to the underlaying value, which can be either a string or an int.