jquery插件ScrollTo

jquery插件ScrollTo，jquery滚动到指定位置，为什么老外的JS就这么牛逼呢？与我自己写起来的插件相差不是一两米啊

/**
 * jQuery.ScrollTo
 * Copyright (c) 2007-2008 Ariel Flesler - aflesler(at)gmail(dot)com | http://flesler.blogspot.com
 * Dual licensed under MIT and GPL.
 * Date: 9/11/2008
 *
 * @projectDescription Easy element scrolling using jQuery.
 * http://flesler.blogspot.com/2007/10/jqueryscrollto.html
 * Tested with jQuery 1.2.6. On FF 2/3, IE 6/7, Opera 9.2/5 and Safari 3. on Windows.
 *
 * @author Ariel Flesler
 * @version 1.4
 *
 * @id jQuery.scrollTo
 * @id jQuery.fn.scrollTo
 * @param {String, Number, DOMElement, jQuery, Object} target Where to scroll the matched elements.
 *	  The different options for target are:
 *		- A number position (will be applied to all axes).
 *		- A string position ('44', '100px', '+=90', etc ) will be applied to all axes
 *		- A jQuery/DOM element ( logically, child of the element to scroll )
 *		- A string selector, that will be relative to the element to scroll ( 'li:eq(2)', etc )
 *		- A hash { top:x, left:y }, x and y can be any kind of number/string like above.
 * @param {Number} duration The OVERALL length of the animation, this argument can be the settings object instead.
 * @param {Object,Function} settings Optional set of settings or the onAfter callback.
 *	 @option {String} axis Which axis must be scrolled, use 'x', 'y', 'xy' or 'yx'.
 *	 @option {Number} duration The OVERALL length of the animation.
 *	 @option {String} easing The easing method for the animation.
 *	 @option {Boolean} margin If true, the margin of the target element will be deducted from the final position.
 *	 @option {Object, Number} offset Add/deduct from the end position. One number for both axes or { top:x, left:y }.
 *	 @option {Object, Number} over Add/deduct the height/width multiplied by 'over', can be { top:x, left:y } when using both axes.
 *	 @option {Boolean} queue If true, and both axis are given, the 2nd axis will only be animated after the first one ends.
 *	 @option {Function} onAfter Function to be called after the scrolling ends. 
 *	 @option {Function} onAfterFirst If queuing is activated, this function will be called after the first scrolling ends.
 * @return {jQuery} Returns the same jQuery object, for chaining.
 *
 * @desc Scroll to a fixed position
 * @example $('div').scrollTo( 340 );
 *
 * @desc Scroll relatively to the actual position
 * @example $('div').scrollTo( '+=340px', { axis:'y' } );
 *
 * @dec Scroll using a selector (relative to the scrolled element)
 * @example $('div').scrollTo( 'p.paragraph:eq(2)', 500, { easing:'swing', queue:true, axis:'xy' } );
 *
 * @ Scroll to a DOM element (same for jQuery object)
 * @example var second_child = document.getElementById('container').firstChild.nextSibling;
 *			$('#container').scrollTo( second_child, { duration:500, axis:'x', onAfter:function(){
 *				alert('scrolled!!');																   
 *			}});
 *
 * @desc Scroll on both axes, to different values
 * @example $('div').scrollTo( { top: 300, left:'+=200' }, { axis:'xy', offset:-20 } );
 */
;(function( $ ){

	var $scrollTo = $.scrollTo = function( target, duration, settings ){
		$(window).scrollTo( target, duration, settings );
	};

	$scrollTo.defaults = {
		axis:'y',
		duration:1
	};

	// Returns the element that needs to be animated to scroll the window.
	// Kept for backwards compatibility (specially for localScroll & serialScroll)
	$scrollTo.window = function( scope ){
		return $(window).scrollable();
	};

	// Hack, hack, hack... stay away!
	// Returns the real elements to scroll (supports window/iframes, documents and regular nodes)
	$.fn.scrollable = function(){
		return this.map(function(){
			// Just store it, we might need it
			var win = this.parentWindow || this.defaultView,
				// If it's a document, get its iframe or the window if it's THE document
				elem = this.nodeName == '#document' ? win.frameElement || win : this,
				// Get the corresponding document
				doc = elem.contentDocument || (elem.contentWindow || elem).document,
				isWin = elem.setInterval;

			return elem.nodeName == 'IFRAME' || isWin && $.browser.safari ? doc.body
				: isWin ? doc.documentElement
				: this;
		});
	};

	$.fn.scrollTo = function( target, duration, settings ){
		if( typeof duration == 'object' ){
			settings = duration;
			duration = 0;
		}
		if( typeof settings == 'function' )
			settings = { onAfter:settings };

		settings = $.extend( {}, $scrollTo.defaults, settings );
		// Speed is still recognized for backwards compatibility
		duration = duration || settings.speed || settings.duration;
		// Make sure the settings are given right
		settings.queue = settings.queue && settings.axis.length > 1;

		if( settings.queue )
			// Let's keep the overall duration
			duration /= 2;
		settings.offset = both( settings.offset );
		settings.over = both( settings.over );

		return this.scrollable().each(function(){
			var elem = this,
				$elem = $(elem),
				targ = target, toff, attr = {},
				win = $elem.is('html,body');

			switch( typeof targ ){
				// A number will pass the regex
				case 'number':
				case 'string':
					if( /^([+-]=)?/d+(px)?$/.test(targ) ){
						targ = both( targ );
						// We are done
						break;
					}
					// Relative selector, no break!
					targ = $(targ,this);
				case 'object':
					// DOMElement / jQuery
					if( targ.is || targ.style )
						// Get the real position of the target 
						toff = (targ = $(targ)).offset();
			}
			$.each( settings.axis.split(''), function( i, axis ){
				var Pos	= axis == 'x' ? 'Left' : 'Top',
					pos = Pos.toLowerCase(),
					key = 'scroll' + Pos,
					old = elem[key],
					Dim = axis == 'x' ? 'Width' : 'Height',
					dim = Dim.toLowerCase();

				if( toff ){// jQuery / DOMElement
					attr[key] = toff[pos] + ( win ? 0 : old - $elem.offset()[pos] );

					// If it's a dom element, reduce the margin
					if( settings.margin ){
						attr[key] -= parseInt(targ.css('margin'+Pos)) || 0;
						attr[key] -= parseInt(targ.css('border'+Pos+'Width')) || 0;
					}

					attr[key] += settings.offset[pos] || 0;

					if( settings.over[pos] )
						// Scroll to a fraction of its width/height
						attr[key] += targ[dim]() * settings.over[pos];
				}else
					attr[key] = targ[pos];

				// Number or 'number'
				if( /^/d+$/.test(attr[key]) )
					// Check the limits
					attr[key] = attr[key] <= 0 ? 0 : Math.min( attr[key], max(Dim) );

				// Queueing axes
				if( !i && settings.queue ){
					// Don't waste time animating, if there's no need.
					if( old != attr[key] )
						// Intermediate animation
						animate( settings.onAfterFirst );
					// Don't animate this axis again in the next iteration.
					delete attr[key];
				}
			});			
			animate( settings.onAfter );			

			function animate( callback ){
				$elem.animate( attr, duration, settings.easing, callback && function(){
					callback.call(this, target, settings);
				});
			};
			function max( Dim ){
				var attr ='scroll'+Dim,
					doc = elem.ownerDocument;

				return win
						? Math.max( doc.documentElement[attr], doc.body[attr]  )
						: elem[attr];
			};
		}).end();
	};

	function both( val ){
		return typeof val == 'object' ? val : { top:val, left:val };
	};

})( jQuery );

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