Scroll = function( target , duration ) {
	this.to = 0;
	this.from = 0;
	if( !duration ) duration = Scroll.DEFAULT_DURATION;
	this.duration = ( duration * Scroll.INTERVAL_TIME );
	this.target = ( !target ) ? document.body : target;
}

Scroll.DEFAULT_DURATION = 1;
Scroll.INTERVAL_TIME = 10;

Scroll.prototype = {
	center: function() {
		this.from = this.getPosition();
		this.to = Math.round( this.getHeight() / 2 );
		this.count = 0;
		var o = this;
		clearInterval( this.interval );
		this.interval = setInterval( function() { o.update(); } , Scroll.INTERVAL_TIME );
	},
	reset: function() {
		this.to = this.from;
		this.from = this.getPosition();
		this.count = 0;
		var o = this;
		clearInterval( this.interval );
		this.interval = setInterval( function() { o.update(); } , Scroll.INTERVAL_TIME );
	},
	
	update: function() {
		var pos = this.ease( this.count++, this.from, this.to - this.from, this.duration );
		this.setPosition( pos );
		if( this.count > this.duration ) {
			this.kill();
		}
	},
	
	ease: function( t , b , c , d ) { 
		return c * t / d + b; // Linear
	},
	
	kill: function() {
		clearInterval( this.interval );
		this.setPosition( this.to );
	},
	
	setPosition: function( pos ) {
		window.scrollTo( 0 , pos );
	},
	
	getPosition: function() {
		if( !window.pageYOffset ) { // IE
			return Math.max( document.body.scrollTop , document.documentElement.scrollTop ); 
		} else { //W3C
			return window.pageYOffset;
		}
	},
	
	getHeight: function() {
		if( !window.innerHeight ) { // IE
			return Math.max( document.body.clientHeight , document.documentElement.clientHeight );
		} else { // W3C
			return window.innerHeight;
		}
	}
};