Introduction
JSON (JavaScript Object Notation) is a standardised text representation for data structures that is widely used for the storage and transfer of data.
JSON is used in several different contexts in TiddlyWiki. For example:
- Tiddlers are represented as JSON data within TiddlyWiki HTML files
- Groups of tiddlers can be exported and imported as JSON files
- Plugin tiddlers store their constituent shadow tiddlers as JSON data
- The client-server configuration uses JSON messages to communicate between the client and the server
- Arbitrary JSON data within DataTiddlers can be processed and manipulated using a set of filter operators and action widgets
About JSON
The technical description of JSON at the official website https://json.org/ is terse. Here we summarise the main features.
JSON supports two basic data structures:
Arrays are lists of items. The items are identified by their numeric index (starting at zero)
An example of an array is:
["one","two","three\"four"]Note the following features of arrays:
- The array is signified by square brackets surrounding the list of items
- Each item is a string in double quotes. Double quotes can be included within the strings by preceding them with a backslash (
\) - The items are separated by commas
Objects are collections of name/value pairs. Each item is a value that is identified by a unique name
An example of an object is:
{
"first": "This is the first value",
"second": "This is the second value",
"third": "This is the third value"
}Note the following features of objects:
- The object is signified by curly braces surrounding the list of name/value pairs
- Each name/value pair consists of the name in double quotes, a colon, and then the value
- The name/value pairs are separated by commas
The examples above all show string values. JSON actually supports several different types of value. Any of these types can be used as a value:
- String values, as shown above
- Numeric values, represented as signed decimals such as
1,3.14. Exponential notation can also be used e.g.-1E10 - Boolean values, represented by the keywords
trueandfalse - The special value
null, which is often used to represent data that is missing or incomplete - Objects and arrays are also values, allowing complex nested structures to be represented