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JSON in TiddlyWiki

 27th April 2022 at 5:47pm

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 true and false
  • 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

Working with Data Tiddlers