JavaScript/Notes/ParameterObject

Passing around lists of parameters? Typechecking arguments? Stop doing that. Here's how to make your code clearer and less error-prone.

The DOM event methods for creating events are an example of what not to do. My comments on w3c DOM mailing list led to the current Event constructor.

Method initTouchEvent (Apple) takes 18 parameter variables. <source lang="javascript"> var touchEvent, canceled;

touchEvent = doc.createEvent("TouchEvent"); if (typeof touchEvent.initTouchEvent == "function") {

 touchEvent.initTouchEvent(type, bubbles, cancelable, view,
 detail, screenX, screenY, pageX, pageY, ctrlKey,
 altKey, shiftKey, metaKey, touches, targetTouches,
 changedTouches, scale, rotation);

   // fire the event
 canceled = target.dispatchEvent(touchEvent);

} </source> 18 parameter variables is too many. It would be much easier can pass in an object that has named property values, and give some defaults for missing property values, such as rotation.

Like this: <source lang="javascript"> Action.touchstart( document.body, {clientX: 330, clientY: 330} ); </source> Where options has a corresponding property for each argument for a single touch event.

<source lang="javascript"> touchstart : function(target, options) {

 return fireTouchEvent("touchstart", target, options);

} </source> <source lang="javascript"> function fireTouchEvent(type, target, options){

   var c = getTouchEventData(target, options),
   doc = target.ownerDocument || target.document || target;
   //setup default values.

   if (!doc || !doc.createTouch) {
       throw TypeError("simulateTouchEvent(): Invalid target.");
   }

   return simulateTouchEvent(doc,
           target, type, c.bubbles, c.cancelable, c.view,
           c.detail, // Not sure what this does in "touch" event.
           c.screenX, c.screenY, c.pageX, c.pageY,
           c.ctrlKey, c.altKey, c.shiftKey, c.metaKey,
           c.touches, c.targetTouches, c.changedTouches, c.scale, c.rotation);

} </source>

Defaults

<source lang="javascript"> function getTouchEventData(target, options) {

 options = options || {};
 var doc = target.ownerDocument || target.document || target;
 return {
   target        : target,
   bubbles       : ("bubbles" in options) ? !!options.bubbles : true,
   cancelable    : ("cancelable" in options) ? !!options.cancelable : true,
   view          : options.view||doc.defaultView,
   detail        : +options.detail||1, // Not sure what this does in "touch" event.
   screenX       : +options.screenX||0,
   screenY       : +options.screenY||0,
   pageX         : +options.pageX||0,
   pageY         : +options.pageY||0,
   ctrlKey       : ("ctrlKey" in options) ? !!options.ctrlKey : false,
   altKey        :  ("altKey" in options) ? !!options.altKey : false,
   shiftKey      : ("shiftKey" in options) ? !!options.shiftKey : false,
   metaKey       : ("metaKey" in options) ? !!options.metaKey : false,
   scale         : +options.scale||1,
   rotation      : +options.rotation||0,
   touches       : createTouchList(options.touches||options),
   targetTouches : createTouchList(options.targetTouches||options),
   changedTouches: createTouchList(options.changedTouches||options)
 };

}</source> See also Too Many Parameters.