TiddlyWiki5/editions/tw5.com/tiddlers/filters/jsontype.tid

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created: 20220611104737314
modified: 20220611104737314
tags: [[Filter Operators]] [[JSON Operators]]
title: jsontype Operator
caption: jsontype
op-purpose: retrieve the type of a property from JSON strings
op-input: a selection of JSON strings
op-parameter: one or more indexes of the property whose type is to be retrieved
op-output: the types of each of the retrieved properties
<<.from-version "5.2.4">> See [[JSON in TiddlyWiki]] for background.
The <<.op jsontype>> operator is used to retrieve the type of a property in JSON data. See also the following related operators:
* <<.olink jsonget>> to retrieve the values of a property in JSON data
* <<.olink jsonindexes>> to retrieve the names of the fields of a JSON object, or the indexes of a JSON array
* <<.olink 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 <<.op jsontype>> operator uses multiple parameters 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"
```
<<.from-version "5.3.2">> Negative indexes into an array are counted from the end, so -1 means the last item, -2 the next-to-last item, and so on:
```
[<jsondata>jsontype[d],[f],[-1]] --> "null"
[<jsondata>jsontype[d],[f],[-2]] --> "boolean"
[<jsondata>jsontype[d],[f],[-4]] --> "string"
```
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 parameter is used to identify the root object. Thus:
```
[<jsondata>jsontype[]] --> "object"
```