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jsontype Operator

 11th June 2022 at 10:47am
purposeretrieve the type of a property from JSON strings
inputa selection of JSON strings
parameterone or more indexes of the property whose type is to be retrieved
outputthe types of each of the retrieved properties
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New in: 5.2.4 See JSON in TiddlyWiki for background.

The jsontype operator is used to retrieve the type of a property in JSON data. See also the following related operators:

  • jsonget to retrieve the values of a property in JSON data
  • jsonindexes to retrieve the names of the fields of a JSON object, or the indexes of a JSON array
  • jsonextract to retrieve a JSON value as a string of JSON

JSON supports the following data types:

  • string - a Unicode string
  • number - a floating point number
  • boolean - Boolean value (true or false)
  • array - an array of values
  • object - an object of name/value pairs
  • null - a special type representing a missing value

Properties within a JSON object are identified by a sequence of indexes. In the following example, the value at [a] is one, and the value at [d][f][0] is five.

{
    "a": "one",
    "b": "",
    "c": "three",
    "d": {
        "e": "four",
        "f": [
            "five",
            "six",
            true,
            false,
            null
        ],
        "g": {
            "x": "max",
            "y": "may",
            "z": "maize"
        }
    }
}

The following examples assume that this JSON data is contained in a variable called jsondata.

The jsontype operator uses multiple operands to specify the indexes of the property whose type is to be retrieved:

[<jsondata>jsontype[a]] --> "string"
[<jsondata>jsontype[d]] --> "object"
[<jsondata>jsontype[d],[f]] --> "array"
[<jsondata>jsontype[d],[f],[2]] --> "boolean"

Indexes can be dynamically composed from variables and transclusions:

[<jsondata>jsontype<variable>,{!!field},[0]]

A subtlety is that the special case of a single blank operand is used to identify the root object. Thus:

[<jsondata>jsontype[]] --> "object"