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JavaScript Object Notation (or JSON)

How to represent data to exchange on the Internet

When exchanging information between different computer systems we need to format the data so that the receiving system can process and understand it. In the history of computer systems many such formats have been created, much to both the delight and despair of programmers. As long as we continue to create information systems we will continue to create data formats.

As we built the web with technologies such as HTML, CSS, and JavaScript we needed a standard to exchange information. In the early days of the internet a format known as XML (Extensible Markup Language) was used to exchange data. In fact, HTML and XML are closely related and as such XML was a good choice. However, over time, XML was found to be a complex format to generate, consume, and for humans to read. Looking for a simpler format that would be easy to generate, consume, and to read. This became JSON.

JSON

JSON stands for the JavaScript Object Notation and is pronounced like the name Jason, as in "Jason and The Argonauts." JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of languages such as C, C#, Java, JavaScript and others.

JSON attempts to be a very simple format with only a few rules. It is built on just two structures:

  • An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.
  • A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.

Values

What kind of values can JSON store?

  • string
  • number
  • booleans
  • null
  • array
  • object

Strings

A simple string in JSON is represented as a sequence of characters surrounded by double quotes:

"This is a JSON string"

Numbers

A number in JSON is represented as an optional - followed by some digits, a decimal place, and digits for the fractional component. Optionally there can be an exponent.

42
-100
42.78
-100.78
6.02214179e+23

Booleans

A true or false value. These are just the literals true and false

Null

Similar to a null in C# or JavaScript, a literal indicating no value. Represented by null

Array

A JSON array simply stores values of various types in a sequence. This could include another array, or an object.

[
100,
42,
99,
4,
"JavaScript",
99,
null,
[9, 8, 7, 6, 5, 4, 3, 2, 1],
false,
{ "score": 100 }
]

Object

A JSON object represents a value that has keys and values. Similar to a C# dictionary, or an object in JavaScript. The format of an object begins with a { and contains key names surrounded by double-quotes, followed by a colon and then followed by any other JSON value type (strings, numbers, booleans, null, an array, or another object). The object closes with a }.

{
"class-size": 5,
"students": ["Mary", "Elizabeth", "Mark", "Sam", "Tom"],
"full": true,
"completed": false
}

Flexibility

The flexibility of the JSON format comes from its simplicity and lack of assumptions about the contents of our data. You will notice that there is no data type for Dates, Times, images, or other more complex structures. These representations of these types of data is up to the developer to specify how they will be represented using the primitive types JSON provides.

Prevalence

JSON has become the lingua-franca, or default, data format on the web. Most systems we receive data from, and send data to, will be using JSON as the data format. As we build backend servers we will be using JSON as our data format.

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