An Introduction to JavaScript Object Notation (JSON)

Introduction

JavaScript Object Notation, or JSON for short, is a lightweight data-interchange format which may prove to be a viable alternative to XML for IT developers. The purpose of a data-interchange format is to transfer information between potentially incompatible technologies. For example, the sender may be a Java application running on Unix and the receiver could be a Visual Basic program running on Windows. In this instance one would require a standardized format to send the data because the applications could not communicate directly with each other. Even if they could, using a protocol such as TCP/IP or FTP, the data structures would have be to be defined somewhere. That's where the data-interchange format comes in. When XML came onto the scene in the late nineties, it was hailed as a godsend by many business managers because it was intuitive to look at and based on the well-known HTML language. Developers, on the other hand, were less impressed. It turns out that parsing XML was not nearly as simple as one might think! Today, despite the proliferation of programming libraries to perform many common tasks, from extracting node attributes to searching for specific data in the hierarchy, programmers are still faced with a learning curve when having to deal with the tags. Web developers faced a similar situation in the early days of dynamic HTML content. Eventually, frameworks such as Struts and Spring provided a way to handle "boiler plate" tag generation. Now, JSON offers developers a more familiar means of structuring data.

Language Overview

JSON's raison d'�tre is to encapsulate an object in a meaningful and standardized way that can be easily understood by humans, as well as being rapidly parsed by machines. This is accomplished by structuring an object as literal representation using common programming syntax characters. Programmers have little difficulty in wrapping their heads around literals because they've been around for a long time. For instance, we almost instinctively know that the following code refers to an integer: "var intType = 3;" whereas this is a String: "var stringType = '3';" (technically a String within a String here!). Most languages can also represent more complex data types like arrays using literals such as: "var arrayLiteral = [1, '2', 3.34, 'dog'];" Notice that the array may contain several data types as well, depending on the language.

Let's get into some specifics regarding the JSON standard.

JSON objects are delimited by curly braces {}. Your initial thought might be that this would confuse the JavaScript interpreter because the curly braces are also used to enclose function bodies. In actuality, operator overloading is a long-standing practice and goes at least as far back to C++. Context is everything, and in each case, there are clues to help identify one from the other. JSON's signature is the key-value pairs used to represent the data, which are each separated by a colon (:):

In the example above, the word "Fred" is enclosed by quotes to denote that it's a String data type, whereas a numeric value does not, as in any programming language. Keys and String values should always be enclosed by double quotes. In my last article, URPM's:AJAX Edition, I made the mistake of not enclosing the keys in quotes. It would seem I'm not alone. Jesse Skinner wrote about this very subject in his article entitled "JSON is not just Object Notation" (see references at the end of the article for a link to the site). It would seem that JSON is a lot pickier about format than JavaScript, as the latter will happily allow you to use single quotes or omit quotes around the keys, as I did. The moral of the story is this: while the JavaScript language provides some flexibility in the construction of Object literals, you may run into issues should you opt to use ready-made JSON parsers. I say may because I didn't encounter any problems when I tested some parsers on my class. Nonetheless, it costs nothing to use the stricter JSON standard.

JSON supports several data types including:

Here is a sample JSON object demonstrating various data types: