Speaking JavaScript

Chapter 22. JSON

JSON (JavaScript Object Notation) is a plain-text format for data storage. It has become quite popular as a data interchange format for web services, for configuration files, and more. ECMAScript 5 has an API for converting from a string in JSON format to a JavaScript value (parsing) and vice versa (stringifying).

Background

This section explains what JSON is and how it was created.

Data Format

JSON stores data as plain text. Its grammar is a subset of the grammar of JavaScript expressions. For example:

{
    "first": "Jane",
    "last": "Porter",
    "married": true,
    "born": 1890,
    "friends": [ "Tarzan", "Cheeta" ]
}

JSON uses the following constructs from JavaScript expressions:

Compound

Objects of JSON data and arrays of JSON data

Atomic

Strings, numbers, booleans, and null

It adheres to these rules:

• Strings must always be double-quoted; string literals such as 'mystr' are illegal.
• Property keys must be double-quoted.

History

Douglas Crockford discovered JSON in 2001. He gave it a name and put up a specification at http://json.org:

I discovered JSON. I do not claim to have invented JSON, because it already existed in nature. What I did was I found it, I named it, I described how it was useful. I don’t claim to be the first person to have discovered it; I know that there are other people who discovered it at least a year before I did. The earliest occurrence I’ve found was, there was someone at Netscape who was using JavaScript array literals for doing data communication as early ...