JSON

JSON: JavaScript Object Notation.

JSON is a syntax for storing and exchanging data.

JSON is text, written with JavaScript object notation.

Exchanging Data

When exchanging data between a browser and a server, the data can only be text.

JSON is text, and we can convert any JavaScript object into JSON, and send JSON to the server.

We can also convert any JSON received from the server into JavaScript objects.

This way we can work with the data as JavaScript objects, with no complicated parsing and translations.

Sending Data

If you have data stored in a JavaScript object, you can convert the object into JSON, and send it to a server:

JSON.stringify()

Receiving Data

If you receive data in JSON format, you can convert it into a JavaScript object:

JSON.parse()

Storing Data

When storing data, the data has to be a certain format, and regardless of where you choose to store it, text is always one of the legal formats.

SON makes it possible to store JavaScript objects as text.

What is JSON?

• JSON stands for JavaScript Object Notation
• JSON is a lightweight data-interchange format
• JSON is "self-describing" and easy to understand
• JSON is language independent *

The JSON format was originally specified by Douglas Crockford.

Why use JSON?

Since the JSON format is text only, it can easily be sent to and from a server, and used as a data format by any programming language.

JavaScript has a built in function to convert a string, written in JSON format, into native JavaScript objects:

JSON.parse()

So, if you receive data from a server, in JSON format, you can use it like any other JavaScript object.

JSON Syntax Rules

The JSON syntax is a subset of the JavaScript syntax.

JSON syntax is derived from JavaScript object notation syntax:

• Data is in name/value pairs
• Data is separated by commas
• Curly braces hold objects
• Square brackets hold arrays

JSON Data - A Name and a Value

JSON data is written as name/value pairs.

A name/value pair consists of a field name (in double quotes), followed by a colon, followed by a value:

"name":"John"

JSON - Evaluates to JavaScript Objects

The JSON format is almost identical to JavaScript objects.

In JSON, keys must be strings, written with double quotes:

JSON

{ "name":"John" }

In JavaScript, keys can be strings, numbers, or identifier names:

JavaScript

{ name:"John" }

JSON Values

In JSON, values must be one of the following data types:

• a string
• a number
• an object (JSON object)
• an array
• a boolean
• null

In JavaScript values can be all of the above, plus any other valid JavaScript expression, including:

• a function
• a date
• undefined

In JSON, string values must be written with double quotes:

JSON

{ "name":"John" }

In JavaScript, you can write string values with double or single quotes:

JavaScript

{ name:'John' }

JSON Uses JavaScript Syntax

Because JSON syntax is derived from JavaScript object notation, very little extra software is needed to work with JSON within JavaScript.

With JavaScript you can create an object and assign data to it, like this:

var person = { name: "John", age: 31, city: "New York" };

JavaScript Arrays as JSON

The same way JavaScript objects can be used as JSON, JavaScript arrays can also be used as JSON.

JSON Files

• The file type for JSON files is ".json"
• The MIME type for JSON text is "application/json"