caption: button
created: 20131024141900000
modified: 20150619111219516
tags: Widgets
title: ButtonWidget
type: text/vnd.tiddlywiki

! Introduction

The button widget displays an HTML `<button>` element that can perform a combination of optional actions when clicked:

* Executing any ActionWidgets that are immediate children of the button widget
* Execute any integrated actions:
** Navigate to a specified tiddler
** Dispatch a user defined [[widget message|Messages]]
** Trigger a user defined [[popup|PopupMechanism]]
** Assign new text to a specified tiddler

The integrated actions are provided as a shortcut for invoking common actions. The same functionality is available via ActionWidgets, with the exception of the support for highlighting selected popups.

! Content and Attributes

The content of the `<$button>` widget is displayed within the button.

|!Attribute |!Description |
|to |The title of the tiddler to navigate to |
|message |The name of the [[widget message|Messages]] to send when the button is clicked |
|param |The optional parameter to the message |
|set |A TextReference to which a new value will be assigned |
|setTo |The new value to assign to the TextReference identified in the `set` attribute |
|popup |Title of a state tiddler for a popup that is toggled when the button is clicked |
|aria-label |Optional [[Accessibility]] label |
|tooltip |Optional tooltip |
|class |An optional CSS class name to be assigned to the HTML element|
|style |An optional CSS style attribute to be assigned to the HTML element |
|selectedClass |An optional additional CSS class to be assigned if the popup is triggered or the tiddler specified in `set` already has the value specified in `setTo`  |
|tag |An optional html tag to use instead of the default "button" |
|default |Default value if `set` tiddler is missing for testing against `setTo` to determine `selectedClass` |

''Note:'' In almost all other cases where a TextReference is used as a widget attribute, it will be placed between curly brackets, to [[transclude|Transclusion in WikiText]] the value currently stored there.  However, when we use a TextReference as the value of a button widget's `set` attribute, we are referencing //the storage location itself//, rather than the value stored there, so we do ''not'' use curly brackets there.  //Example:// we could code a button widget that sets the `caption` field of TiddlerA to be the same as that of TiddlerB as:

```
<$button set="TiddlerA!!caption" setTo={{TiddlerB!!caption}} >

Press me!

</$button>
```

''Tip:'' Set ''class'' to `tc-btn-invisible tc-tiddlylink` to have a button look like an internal link.