created: 20220427174702859
modified: 20220427171449102
tags: [[JSON in TiddlyWiki]] Learning
title: Reading data from JSON tiddlers
type: text/vnd.tiddlywiki

See [[JSON in TiddlyWiki]] for an overview of using JSON in TiddlyWiki.

!! Introduction

The following examples assume the following JSON data structure is stored in a data tiddler called "foobar" with the type `application/json`:

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

!! Text References for Accessing JSON Data

[[Text references|TextReference]] are a simple shortcut syntax to look up the value of a named property. For example, if a [[DictionaryTiddler|DictionaryTiddlers]] called `MonthDays` contains:

```
oct:31
nov:30
dec:31
```

... then `{{MonthDays##nov}}` will resolve to the value `30`.

The same is true if `MonthDays` is a [[JSONTiddler|JSONTiddlers]] with the following content:

```
{"oct":31,"nov":30,"dec":31}
```

!! Operators for Reading JSON Data

Values are identified by a sequence of indexes. For example, the value at `[a]` is `one`, and the value at `[d][f][0]` is `five`.

The new operators use multiple operands to specify the indexes:

```
[[foobar]jsonget[a]] --> "one"
[[foobar]jsonget[d],[e]] --> "four"
[[foobar]jsonget[d],[f],[0]] --> "five"
```

Indexes can be dynamically composed from variables and transclusions:

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

Boolean values and null are returned as normal strings. The [[jsontype Operator]] returns a string identifying the original type. Thus:

```
[[foobar]jsontype[a]] --> "string"
[[foobar]jsontype[d]] --> "object"
[[foobar]jsontype[d],[f]] --> "array"
[[foobar]jsontype[d],[f],[2]] --> "boolean"
```

Using the [[jsonget Operator]] to retrieve an object or an array returns a list of all the values. For example:

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

The [[jsonindexes Operator]] retrieves the corresponding indexes:

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

The behaviour when retrieving an object or array that contains values that are themselves objects or arrays may be confusing: the object is read recursively as a list of values. For example:

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

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

```
[[foobar]jsonindexes[]] --> "a", "b", "c", "d"
```

An example of using a list widget to iterate through the properties of an array within a JSON object:

```
<$list filter="[[foobar]jsonindexes[d][f]]">
    <div>
        <$text text=<<currentTiddler>>/>: <$text text={{{ [[foobar]jsonget[d][f]<currentTiddler>]  }}}/>
    </div>
</$list>

Prints:

0: five
1: six
2: true
3: false
4: null
```