jQuery ui 1.8.6 position 的一个bug

在开发widget的时候，发现了一个jquery ui position的一个bug。这个bug是有关collision的。这个功能就是当当前的定位的元素超出屏幕屏幕的时候，会自动翻转定位。比如说定位在右边，而右边不够显示定位元素的时候，就定位到左边。

下面我贴出代码来分析position的代码以及这个bug出现的位置。

 

/*
 * jQuery UI Position 1.8.6
 *
 * Copyright 2010, AUTHORS.txt (http://jqueryui.com/about)
 * Dual licensed under the MIT or GPL Version 2 licenses.
 * http://jquery.org/license
 *
 * http://docs.jquery.com/UI/Position
 */
(function( $, undefined ) {

$.ui = $.ui || {};

var horizontalPositions = /left|center|right/,
	verticalPositions = /top|center|bottom/,
	center = "center",
	_position = $.fn.position,
	_offset = $.fn.offset;

$.fn.position = function( options ) {
	if ( !options || !options.of ) {
		return _position.apply( this, arguments );
	}

	// make a copy, we don't want to modify arguments
	options = $.extend( {}, options );

	var target = $( options.of ),
		targetElem = target[0],
		collision = ( options.collision || "flip" ).split( " " ),
		offset = options.offset ? options.offset.split( " " ) : [ 0, 0 ],
		targetWidth,
		targetHeight,
		basePosition;
　　　　//如果相对定位的元素是document元素的话
	if ( targetElem.nodeType === 9 ) {
		targetWidth = target.width();
		targetHeight = target.height();
		basePosition = { top: 0, left: 0 };
	// TODO: use $.isWindow() in 1.9
	} else if ( targetElem.setTimeout ) {
		targetWidth = target.width();
		targetHeight = target.height();
		basePosition = { top: target.scrollTop(), left: target.scrollLeft() };
	} else if ( targetElem.preventDefault ) {
		// force left top to allow flipping
		options.at = "left top";
		targetWidth = targetHeight = 0;
		basePosition = { top: options.of.pageY, left: options.of.pageX };
	} else {
		targetWidth = target.outerWidth();
		targetHeight = target.outerHeight();
		basePosition = target.offset();
	}

	// force my and at to have valid horizontal and veritcal positions
	// if a value is missing or invalid, it will be converted to center 
	$.each( [ "my", "at" ], function() {
		var pos = ( options[this] || "" ).split( " " );
		if ( pos.length === 1) {
			pos = horizontalPositions.test( pos[0] ) ?
				pos.concat( [center] ) :
				verticalPositions.test( pos[0] ) ?
					[ center ].concat( pos ) :
					[ center, center ];
		}
		pos[ 0 ] = horizontalPositions.test( pos[0] ) ? pos[ 0 ] : center;
		pos[ 1 ] = verticalPositions.test( pos[1] ) ? pos[ 1 ] : center;
		options[ this ] = pos;
	});

	// normalize collision option
	if ( collision.length === 1 ) {
		collision[ 1 ] = collision[ 0 ];
	}

	// normalize offset option
	offset[ 0 ] = parseInt( offset[0], 10 ) || 0;
	if ( offset.length === 1 ) {
		offset[ 1 ] = offset[ 0 ];
	}
	offset[ 1 ] = parseInt( offset[1], 10 ) || 0;

	if ( options.at[0] === "right" ) {
		basePosition.left += targetWidth;
	} else if (options.at[0] === center ) {
		basePosition.left += targetWidth / 2;
	}

	if ( options.at[1] === "bottom" ) {
		basePosition.top += targetHeight;
	} else if ( options.at[1] === center ) {
		basePosition.top += targetHeight / 2;
	}

	basePosition.left += offset[ 0 ];
	basePosition.top += offset[ 1 ];

	return this.each(function() {
		var elem = $( this ),
			elemWidth = elem.outerWidth(),
			elemHeight = elem.outerHeight(),
			marginLeft = parseInt( $.curCSS( this, "marginLeft", true ) ) || 0,
			marginTop = parseInt( $.curCSS( this, "marginTop", true ) ) || 0,

　　　　　　　　　//此处就是出现问题的地方，在ie下面如果当前元素的margin没有设置或者设置为auto的话，在取$.curCss(this,"marginRight",true)的时候会去取出为
　　　　　　　　　//"auto"，此问题在其他的浏览器下，不会取出为auto，而是当前元素的css实际值。,在转换的时候会为NAN，这个时候再做前面的运算，都将为NAN，
　　　　　　　　　//最终此值将被计算为0. 而这样，在下面做反转的时候，将会计算出错误的值，而不会发生发转。目前的解决方法就是在当前的元素上加上
　　　　　　　　　//margin-right和margin-bottom的值。　 

			collisionWidth = elemWidth + marginLeft +
				parseInt( $.curCSS( this, "marginRight", true ) ) || 0,
			collisionHeight = elemHeight + marginTop +
				parseInt( $.curCSS( this, "marginBottom", true ) ) || 0,
			position = $.extend( {}, basePosition ),
			collisionPosition;

		if ( options.my[0] === "right" ) {
			position.left -= elemWidth;
		} else if ( options.my[0] === center ) {
			position.left -= elemWidth / 2;
		}

		if ( options.my[1] === "bottom" ) {
			position.top -= elemHeight;
		} else if ( options.my[1] === center ) {
			position.top -= elemHeight / 2;
		}

		// prevent fractions (see #5280)
		position.left = parseInt( position.left );
		position.top = parseInt( position.top );

		collisionPosition = {
			left: position.left - marginLeft,
			top: position.top - marginTop
		};

		$.each( [ "left", "top" ], function( i, dir ) {
			if ( $.ui.position[ collision[i] ] ) {
				$.ui.position[ collision[i] ][ dir ]( position, {
					targetWidth: targetWidth,
					targetHeight: targetHeight,
					elemWidth: elemWidth,
					elemHeight: elemHeight,
					collisionPosition: collisionPosition,
					collisionWidth: collisionWidth,
					collisionHeight: collisionHeight,
					offset: offset,
					my: options.my,
					at: options.at
				});
			}
		});

		if ( $.fn.bgiframe ) {
			elem.bgiframe();
		}
		elem.offset( $.extend( position, { using: options.using } ) );
	});
};
//此处就是做翻转的函数的。
$.ui.position = {
	fit: {
		left: function( position, data ) {
			var win = $( window ),
				over = data.collisionPosition.left + data.collisionWidth - win.width() - win.scrollLeft();
			position.left = over > 0 ? position.left - over : Math.max( position.left - data.collisionPosition.left, position.left );
		},
		top: function( position, data ) {
			var win = $( window ),
				over = data.collisionPosition.top + data.collisionHeight - win.height() - win.scrollTop();
			position.top = over > 0 ? position.top - over : Math.max( position.top - data.collisionPosition.top, position.top );
		}
	},

	flip: {
		left: function( position, data ) {
			if ( data.at[0] === center ) {
				return;
			}
			var win = $( window ),
				over = data.collisionPosition.left + data.collisionWidth - win.width() - win.scrollLeft(),
				myOffset = data.my[ 0 ] === "left" ?
					-data.elemWidth :
					data.my[ 0 ] === "right" ?
						data.elemWidth :
						0,
				atOffset = data.at[ 0 ] === "left" ?
					data.targetWidth :
					-data.targetWidth,
				offset = -2 * data.offset[ 0 ];
			position.left += data.collisionPosition.left < 0 ?
				myOffset + atOffset + offset :
				over > 0 ?
					myOffset + atOffset + offset :
					0;
		},
		top: function( position, data ) {
			if ( data.at[1] === center ) {
				return;
			}
			var win = $( window ),
				over = data.collisionPosition.top + data.collisionHeight - win.height() - win.scrollTop(),
				myOffset = data.my[ 1 ] === "top" ?
					-data.elemHeight :
					data.my[ 1 ] === "bottom" ?
						data.elemHeight :
						0,
				atOffset = data.at[ 1 ] === "top" ?
					data.targetHeight :
					-data.targetHeight,
				offset = -2 * data.offset[ 1 ];
			position.top += data.collisionPosition.top < 0 ?
				myOffset + atOffset + offset :
				over > 0 ?
					myOffset + atOffset + offset :
					0;
		}
	}
};

// offset setter from jQuery 1.4
if ( !$.offset.setOffset ) {
	$.offset.setOffset = function( elem, options ) {
		// set position first, in-case top/left are set even on static elem
		if ( /static/.test( $.curCSS( elem, "position" ) ) ) {
			elem.style.position = "relative";
		}
		var curElem   = $( elem ),
			curOffset = curElem.offset(),
			curTop    = parseInt( $.curCSS( elem, "top",  true ), 10 ) || 0,
			curLeft   = parseInt( $.curCSS( elem, "left", true ), 10)  || 0,
			props     = {
				top:  (options.top  - curOffset.top)  + curTop,
				left: (options.left - curOffset.left) + curLeft
			};
		
		if ( 'using' in options ) {
			options.using.call( elem, props );
		} else {
			curElem.css( props );
		}
	};

	$.fn.offset = function( options ) {
		var elem = this[ 0 ];
		if ( !elem || !elem.ownerDocument ) { return null; }
		if ( options ) { 
			return this.each(function() {
				$.offset.setOffset( this, options );
			});
		}
		return _offset.call( this );
	};
}

}( jQuery ));