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.

Refactoring

Method initTouchEvent (Apple) takes 18 parameter variables. It is hard to remember the order and type of each and every variable.

// 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);
}

Pass an Object

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:

Action.touchstart( document.body, {clientX: 330, clientY: 330} );

Where options has a corresponding property for each argument for a single touch event.

touchstart : function(target, options) {
  return fireTouchEvent("touchstart", target, options);
}

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);
}

Defaults

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)
  };
}

See also Too Many Parameters.