created: 20201123113532200
modified: 20250817151316712
tags: Widgets TriggeringWidgets
title: EventCatcherWidget
type: text/vnd.tiddlywiki

! Introduction

<<.from-version "5.1.23">>

//This is an advanced widget intended for use by those familiar with HTML, CSS and JavaScript handling of DOM events.//

The event catcher widget traps DOM-initiated Javascript events dispatched within its child content, and allows invoking a series of ActionWidgets in response to those events.

In order for the events to be trapped:

* The event must be of one of the events specified in the event catcher widget's `events` attribute
* The event must target a DOM node with an ancestor that matches the widget's `selector` attribute
* <<.from-version "5.2.2">> Optionally, the DOM node targeted by the event must also match the widgets `matchSelector` attribute
* The event must support event bubbling

Use of the event catcher widget is beneficial when using large numbers of other trigger widgets such as the ButtonWidget is causing performance problems. The workflow it enables is akin to what is referred to as "event delegation" in JavaScript parlance.

! Content and Attributes

The content of the `<$eventcatcher>` widget is displayed normally.

|!Attribute |!Description |
|selector |A CSS selector. Only events originating inside a DOM node with this selector will be trapped |
|matchSelector |<<.from-version "5.2.2">> An optional CSS selector. Only events targeting DOM nodes matching this selector will be trapped |
|//{any attributes starting with $}// |<<.from-version "5.2.0">> Each attribute name (excluding the $) specifies the name of an event, and the value specifies the action string to be invoked. For example: `$click=<<clickActions>>`  |
|tag |Optional. The HTML element the widget creates to capture the events, defaults to:<br>» `span` when parsed in inline-mode<br>» `div` when parsed in block-mode |
|class |Optional. A CSS class name (or names) to be assigned to the widget HTML element |
|stopPropagation |<<.from-version "5.2.0">> Optional. Set to "always" to always stop event propagation even if there are no corresponding actions to invoke, "never" to never stop event propagation, or the default value "onaction" with which event propagation is only stopped if there are corresponding actions that are invoked. |
|//events// |//(removed – see below)// Space separated list of JavaScript events to be trapped, for example "click" or "click dblclick" |
|//actions-*// |//(removed – see below)// Action strings to be invoked when a matching event is trapped. Each event is mapped to an action attribute name of the form <code>actions-<em>event</em></code> where <code><em>event</em></code> represents the type of the event. For example: `actions-click` or `actions-dblclick` |

<<.from-version "5.4.0">> The attributes `events` and `actions-*` have been removed as they are no longer needed. Instead you can use attributes starting with $ where the attribute name (excluding the $) specifies the name of the event and the value specifies the action string to be invoked. If any attributes with the prefix $ are present then the `types` attribute is ignored.

! Variables

The following variables are made available to the actions:

|!Variables |!Description |
|`dom-*` |All DOM attributes of the node matching the given selector are made available as variables, with the prefix `dom-` |
|`modifier` |The [[modifier Variable]] contains the Modifier Key held during the event (can be "normal", "ctrl", "shift", "alt" or combinations thereof) |
|`event-mousebutton` |The mouse button (if any) used to trigger the event (can be "left", "right" or "middle"). Note that not all event types support the mousebutton property.  <<.infoBox """This property only guarantees to indicate which buttons are pressed during events caused by pressing or releasing one or multiple buttons. As such, it is not reliable for events such as mouseenter, mouseleave, mouseover, mouseout, or mousemove. More details at: https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/button""">> |
|`event-type` |The type property of the JavaScript event.  |
|`event-detail-*` |Any properties in the detail attribute of the event are made available with the prefix `event-detail-` |
|`tv-popup-coords` |A relative co-ordinate string that can be used with the ActionPopupWidget to trigger a popup at the DOM node matching the selector where the event originated (see [[Coordinate Systems]] for more information) |
|`tv-popup-abs-coords` |<<.from-version "5.2.4">> An absolute co-ordinate string that can be used with the ActionPopupWidget to trigger a popup at the DOM node matching the selector where the event originated (see [[Coordinate Systems]] for more information) |
|`tv-widgetnode-width` |<<.from-version "5.2.3">> `offsetWidth` of the DOM node created by the eventcatcher widget |
|`tv-widgetnode-height` |<<.from-version "5.2.3">> `offsetHeight` of the DOM node created by the eventcatcher widget |
|`tv-selectednode-posx` |`x` offset position of the selected DOM node |
|`tv-selectednode-posy` |`y` offset position of the selected DOM node  |
|`tv-selectednode-width` |`offsetWidth` of the selected DOM node |
|`tv-selectednode-height` |`offsetHeight` of the selected DOM node |
|`event-fromselected-posx` |`x` position of the event relative to the selected DOM node |
|`event-fromselected-posy` |`y` position of the event relative to the selected DOM node |
|`event-fromcatcher-posx` |`x` position of the event relative to the event catcher DOM node |
|`event-fromcatcher-posy` |`y` position of the event relative to the event catcher DOM node |
|`event-fromviewport-posx` |<<.from-version "5.2.0">> `x` position of the event relative to the viewport |
|`event-fromviewport-posy` |<<.from-version "5.2.0">> `y` position of the event relative to the viewport |

! Example

This example uses the ActionLogWidget and will log the `data-item-id` attribute of the clicked DOM node to the browser's JavaScript [[console|Web Developer Tools]]

```
\define clickactions()
<$action-log item=<<dom-data-item-id>> event=<<event-type>>/>
\end

\define contextmenu-actions()
<$action-log item=<<dom-data-item-id>> event=<<event-type>>/>
\end

<$eventcatcher selector=".item" $click=<<clickactions>> $contextmenu=<<contextmenu-actions>> tag="div">

<div class="item" data-item-id="item1">
Click events here will be trapped
</div>

<div class="item" data-item-id="item2">
And here too
</div>

<div data-item-id="item3">
Not here
</div>

<div class="item" data-item-id="item4">
And here
</div>

</$eventcatcher>
```
