JavaScript/Notes/ParameterObject

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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.

Refactoring[edit]

Method initTouchEvent (Apple) takes 18 parameter variables. It is hard to remember the order and type of each and every variable. <source lang="javascript"> // Note: This code is iOS specific! var touchEvent, canceled;

touchEvent = document.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>

Pass an Object[edit]

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[edit]

<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.