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jsonget Operator

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

The jsonget operator is used to retrieve values from JSON data as strings. See also the following related operators:

  • jsontype to retrieve the type of a JSON value
  • 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

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 jsonget operator uses multiple operands to specify the indexes of the property to retrieve:

[<jsondata>jsonget[a]] --> "one"
[<jsondata>jsonget[d],[e]] --> "four"
[<jsondata>jsonget[d],[f],[0]] --> "five"

Indexes can be dynamically composed from variables and transclusions:

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

Boolean values and null are returned as normal strings. The jsontype operator can be used to retrieve a string identifying the original type. Thus:

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

Using the jsonget operator to retrieve an object or an array returns a list of the values. For example:

[<jsondata>jsonget[d],[f]] --> "five","six","true","false","null"
[<jsondata>jsonget[d],[g]] --> "max","may","maize"

The jsonindexes operator retrieves the corresponding indexes:

[<jsondata>jsonindexes[d],[f]] --> "0", "1", "2", "3", "4"
[<jsondata>jsonindexes[d],[g]] --> "x", "y", "z"

If the object or array contains nested child objects or arrays then the values are retrieved recursively and returned flattened into a list. For example:

[<jsondata>jsonget[d]] --> "four","five","six","true","false","null","max","may","maize"

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

[<jsondata>jsonindexes[]] --> "a", "b", "c", "d"