Can someone please tell me why

1

why isn’t the alpha de-incrementing/incrementing in integers with this prototype even when i send it an integer for the argument vel? In the following example shouldn’t it be de-incrementing/incrementing by 5s?

MovieClip.prototype.alpha = function(vel, to) {
	this.vel = vel;
	this.to = to;
	this.alpha_init = this._alpha;
	this.onEnterFrame = function() {
		updateAfterEvent();
		if (this.to != undefined && this.vel != undefined) {
			if (this.to>this.alpha_init) {
				if (this._alpha<=100) {
					this._alpha += this.vel;
				} else {
					this.onEnterFrame = null;
				}
			} else {
				if (this._alpha>this.to) {
					this._alpha -= this.vel;
					trace("this._alpha is: "+this._alpha);
					trace("this.vel is: "+this.vel);
				} else {
					this.onEnterFrame = null;
				}
			}
		} else {
		}
	};
};
box_mc.onPress = function() {
	this.alpha(5, 0);
};