Chapter 18: Scripting

Contents

• • 18.1. The ‘script’ element
  • 18.2. Event handling
  • 18.3. Event attributes
    • 18.3.1. Event attribute for the SVGLoad event
    • 18.3.2. Event attributes on graphics and container elements
    • 18.3.3. Document-level event attributes
    • 18.3.4. Animation event attributes
  • 18.4. DOM interfaces
    • 18.4.1. Interface SVGScriptElement
    • 18.4.2. Interface SVGZoomEvent

18.1. The ‘script’ element

A ‘script’ element is equivalent to the ‘script’ element in HTML and thus is the place for scripts (e.g., ECMAScript). Any functions defined within any ‘script’ element have a "global" scope across the entire current document.

Example script01 defines a function circle_click which is called by the ‘onclick’ event attribute on the ‘circle’ element. The drawing below on the left is the initial image. The drawing below on the right shows the result after clicking on the circle.

Note that this example demonstrates the use of the ‘onclick’ event attribute for explanatory purposes. The example presupposes the presence of an input device with the same behavioral characteristics as a mouse, which will not always be the case. To support the widest range of users, the ‘onactivate’ event attribute should be used instead of the ‘onclick’ event attribute.

Before attempting to execute the ‘script’ element the resolved media type value for ‘type’ must be inspected. If the SVG user agent does not support the scripting language then the ‘script’ element must not be executed.

<?xml version="1.0" standalone="no"?>
<svg width="6cm" height="5cm" viewBox="0 0 600 500"
     xmlns="http://www.w3.org/2000/svg" version="1.1">
  <desc>Example script01 - invoke an ECMAScript function from an onclick event
  </desc>
  <!-- ECMAScript to change the radius with each click -->
  <script type="application/ecmascript"> <![CDATA[
    function circle_click(evt) {
      var circle = evt.target;
      var currentRadius = circle.getAttribute("r");
      if (currentRadius == 100)
        circle.setAttribute("r", currentRadius*2);
      else
        circle.setAttribute("r", currentRadius*0.5);
    }
  ]]> </script>

  <!-- Outline the drawing area with a blue line -->
  <rect x="1" y="1" width="598" height="498" fill="none" stroke="blue"/>

  <!-- Act on each click event -->
  <circle onclick="circle_click(evt)" cx="300" cy="225" r="100"
          fill="red"/>

  <text x="300" y="480" 
        font-family="Verdana" font-size="35" text-anchor="middle">

    Click on circle to change its size
  </text>
</svg>

Example script01

View this example as SVG (SVG-enabled browsers only)

18.2. Event handling

Events can cause scripts to execute when either of the following has occurred:

• Event attributes such as ‘onclick’ or ‘onload’ are assigned to particular elements, where the values of the event attributes are script which is executed when the given event occurs.
• Event listeners as described in DOM Level 2 Events [DOM2EVENTS] are defined which are invoked when a given event happens on a given object.

Related sections of the spec:

• User interface events describes how an SVG user agent handles events such as pointer movements events (e.g., mouse movement) and activation events (e.g., mouse click).
• Relationship with DOM2 events describes what parts of DOM are supported by SVG and how to register event listeners.

18.3. Event attributes

The following event attributes are available on many SVG elements.

The complete list of events that are part of the SVG language and SVG DOM and descriptions of those events is provided in Complete list of supported events.

The contents of event attributes are always interpreted as ECMAScript, as if processed with the media type 'application/ecmascript'. [RFC2046][RFC4329]

18.3.1. Event attribute for the SVGLoad event

Below is the definition for the ‘onload’ event attribute. It can be specified on all of the animation elements and most of the graphics elements and container elements. The ‘onload’ event attribute is classified as both a graphical event attribute and an animation event attribute. (See the definition for each element to determine whether it can have a graphical event attribute specified on it.)

18.3.2. Event attributes on graphics and container elements

Below are the definitions for the graphical event attributes. These can be specified on most graphics elements and container elements. (See the definition for each element to determine whether it can have a graphical event attribute specified on it.)

Note that ‘onload’, defined above, is also classified as a graphical event attribute.

18.3.3. Document-level event attributes

Below are the definitions for the document event attributes. These can be specified only on ‘svg’ elements.

The conformance class for the 'only-on-<svg> elements' criteria needs to be clarified here (this is for document validation presumably, so perhaps Conforming SVG Document Fragments would be appropriate to mention), the document event attributes should be fine to specify on any element, they just don't do much in all such cases, and it makes sense to not encourage uses where it doesn't have any real meaning. For Conforming Dynamic SVG Viewers: what the document event attributes should do is register an event listener for the event in question.

'onerror' should be available on image, script and elements that load external resources. This is related to issue 2254.

18.3.4. Animation event attributes

Below are the definitions for the animation event attributes. These can be specified on the animation elements.

Note that ‘onload’, defined above, is also classified as an animation event attribute.

18.4. DOM interfaces

18.4.1. Interface SVGScriptElement

The SVGScriptElement interface corresponds to the ‘script’ element.

interface SVGScriptElement : SVGElement {
  attribute DOMString type;
};

SVGScriptElement implements SVGURIReference;

Attributes:

type (DOMString)

Corresponds to attribute ‘type’ on the given ‘script’ element.

18.4.2. Interface SVGZoomEvent

A DOM consumer can use the hasFeature of the DOMImplementation interface to determine whether the SVG zoom event set has been implemented by a DOM implementation. The feature string for this event set is "SVGZoomEvents". This string is also used with the createEvent method.

The zoom event handler occurs before the zoom event is processed. The remainder of the DOM represents the previous state of the document. The document will be updated upon normal return from the event handler.

The UI event type for a zoom event is:

SVGZoom

The zoom event occurs when the user initiates an action which causes the current view of the SVG document fragment to be rescaled. Event handlers are only recognized on ‘svg’ elements. See SVGZoom event.

• Bubbles: Yes
• Cancelable: No
• Context Info: zoomRectScreen, previousScale, previousTranslate, newScale, newTranslate, screenX, screenY, clientX, clientY, altKey, ctrlKey, shiftKey, metaKey, relatedNode.
  (screenX, screenY, clientX and clientY indicate the center of the zoom area, with clientX and clientY in viewport coordinates for the corresponding ‘svg’ element. relatedNode is the corresponding ‘svg’ element.)

interface SVGZoomEvent : UIEvent {
  readonly attribute SVGRect zoomRectScreen;
  readonly attribute float previousScale;
  readonly attribute SVGPoint previousTranslate;
  readonly attribute float newScale;
  readonly attribute SVGPoint newTranslate;
};

Attributes:

zoomRectScreen (readonly SVGRect)

The specified zoom rectangle in screen units.

The SVGRect object is read only.

previousScale (readonly float)

The scale factor from previous zoom operations that was in place before the zoom operation occurred.

previousTranslate (readonly SVGPoint)

The translation values from previous zoom operations that were in place before the zoom operation occurred.

The SVGPoint object is read only.

newScale (readonly float)

The scale factor that will be in place after the zoom operation has been processed.

newTranslate (readonly SVGPoint)

The translation values that will be in place after the zoom operation has been processed.

The SVGPoint object is read only.