JSON Datatypes

JSON data structures can include any of the following types of data:

• q String

• q Number

• q Boolean value (true/false)

• q null

• q Object

• q Array

JSON strings must be double-quoted. They use standard JavaScript escape codes and add a backslash before the following characters:

• q “ (quotation marks)

• q b (backspace)

• q n (new line)

• q f (form feed)

• q r (carriage return)

• q t (horizontal tab)

• q u (plus 4 digits for a Unicode character)

• q \ (backslash)

• q / (forward slash)

For example, to represent the string I feel “funny”, you escape both sets of quotation marks around the word funny:

     "I feel \"funny\""

Object Literals

JavaScript objects can be defined using an object constructor or an object literal. To define a new object with a constructor, you use the Object constructor function with the new keyword.

     var member = new Object();

Then you can add properties to the object using dot notation.

     member.name = "James";
     member.address = "32 Smith Rd";
     member.isRegistered = true;

You can also add properties to the object using array syntax.

     member["name"] = "James";
     member["address"] = "325 Smith Rd";
     member["isRegistered"] = true;

You can create the same object more efficiently by using an object literal.

     var member =
     {name: "James",
     address: "32 Smith Road",
     isRegistered: true
     };

JSON doesn’t use constructors, only literals. The following code shows the member object formulated as JSON text:

     {"name": "James",
       "address": "32 Smith Road",
       "isRegistered": true
     }

Array Literals
JavaScript arrays can also be created using
a constructor or using an array literal.
To define a new array with a constructor,
you use the Array constructor function with the new keyword.
     var myArray = new Array();
Then, you can add members to the array using square brackets
and an index value that indicates the position in the array.
     myArray[0] = 1218;
     myArray[1] = "1000"
     myArray[2] = "james";
You can create the same object more efficiently using
an array literal.
     var myArray = [1218, "Crawford", "Drive"];
The following code shows this array formulated as JSON text:
     [1218, "1000", "James"]

Using a JSON Parser
You can use a JSON parser to create JSON text from
objects and arrays, and to create objects and arrays
from JSON text. A JSON parser is provided on the
JSON site at http://www.json.org/json.js.
You can copy this JavaScript file and reference it in your
page by including this code in the head section of the page:
     <script type="text/javascript" src="json.js"></script>
It defines two functions:
toJSONString()
parseJSON()
The toJSONString() method is added to the JavaScript
Object and Array definitions, and it enables you to
convert a JavaScript object or array to JSON text.
The object or array doesn't need to be preformulated as
a literal in order to use this method. For example, the
following code for the member object uses the Object constructor:
     <script type="text/javascript">
     var member = new Object();
     member.name = "James";
     member.address = "32 Smith Rd";
     member.isRegistered = true;
     member = member.toJSONString();
     alert("The member object as a JSON data structure: \n" + member);
     </script>