Prototype1.5 rc2版指南最后一篇之Position

Position是prototype中定义的一个对象，提供了操作DOM中与位置相关的方法，要很好的理解元素在页面中的位置，可以参考这篇文章：Relatively Absolute 具体代码如下，按照代码说说，其中英文是作者的注释，中文红色的才是偶的说明或翻译英文的注释，采用顶式注释法(注释在要说明的代码的上面)说明 // set to true if needed, warning: firefox performance problems // NOT neeeded for page scrolling, only if draggable contained in // scrollable elements //只有在使用拖动的时候元素包含在有滚动条的元素中才需要设置为true includeScrollOffsets: false, // must be called before calling withinIncludingScrolloffset, every time the // page is scrolled //当页面被scrolled后，使用withinIncludingScrolloffset的时候需要先调用这个方法 prepare: function() { //横向滚动条滚动的距离 this.deltaX = window.pageXOffset || document.documentElement.scrollLeft || document.body.scrollLeft || 0; //纵向滚动条滚动的距离 this.deltaY = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop || 0; }, //元素由于滚动条偏移的总距离 realOffset: function(element) { var valueT = 0, valueL = 0; do { valueT += element.scrollTop || 0; valueL += element.scrollLeft || 0; element = element.parentNode; } while (element); return [valueL, valueT]; }, //元素在页面中由offsetParent累积的offset，当offsetParent都没有滚动条时，就是元素在页面中的位置cumulativeOffset: function(element) { var valueT = 0, valueL = 0; do { valueT += element.offsetTop || 0; valueL += element.offsetLeft || 0; element = element.offsetParent; } while (element); return [valueL, valueT]; }, //元素相对于containing block("nearest positioned ancestor")的位置，也就是相对于最近的一个position设置为relative或者absolute的祖先节点的位置，如果没有就是相对于body的位置，跟style.top，style.left一样？positionedOffset: function(element) { var valueT = 0, valueL = 0; do { valueT += element.offsetTop || 0; valueL += element.offsetLeft || 0; element = element.offsetParent; if (element) { if(element.tagName=='BODY') break; var p = Element.getStyle(element, 'position'); if (p == 'relative' || p == 'absolute') break; } } while (element); return [valueL, valueT]; }, //offsetParent offsetParent: function(element) { if (element.offsetParent) return element.offsetParent; if (element == document.body) return element; while ((element = element.parentNode) && element != document.body) if (Element.getStyle(element, 'position') != 'static') return element; return document.body; }, // caches x/y coordinate pair to use with overlap //判断指定的位置是否在元素内 within: function(element, x, y) { if (this.includeScrollOffsets) return this.withinIncludingScrolloffsets(element, x, y); this.xcomp = x; this.ycomp = y; this.offset = this.cumulativeOffset(element); return (y >= this.offset[1] && y < this.offset[1] + element.offsetHeight && x >= this.offset[0] && x < this.offset[0] + element.offsetWidth); }, //跟within差不多，不过考虑到滚动条，也许是在元素上面，但不是直接在上面，因为滚动条也许已经使元素不可见了 withinIncludingScrolloffsets: function(element, x, y) { var offsetcache = this.realOffset(element); this.xcomp = x + offsetcache[0] - this.deltaX; this.ycomp = y + offsetcache[1] - this.deltaY; this.offset = this.cumulativeOffset(element); return (this.ycomp >= this.offset[1] && this.ycomp < this.offset[1] + element.offsetHeight && this.xcomp >= this.offset[0] && this.xcomp < this.offset[0] + element.offsetWidth); }, // within must be called directly before //在调用这个方法前，必须先调用within，返回在with指定的位置在水平或者垂直方向上占用的百分比 overlap: function(mode, element) { if (!mode) return 0; if (mode == 'vertical') return ((this.offset[1] + element.offsetHeight) - this.ycomp) / element.offsetHeight; if (mode == 'horizontal') return ((this.offset[0] + element.offsetWidth) - this.xcomp) / element.offsetWidth; }, //返回元素相对页面的真实位置 page: function(forElement) { var valueT = 0, valueL = 0; var element = forElement; do { valueT += element.offsetTop || 0; valueL += element.offsetLeft || 0; // Safari fix if (element.offsetParent==document.body) if (Element.getStyle(element,'position')=='absolute') break; } while (element = element.offsetParent); element = forElement; do { if (!window.opera || element.tagName=='BODY') { valueT -= element.scrollTop || 0; valueL -= element.scrollLeft || 0; } } while (element = element.parentNode); return [valueL, valueT]; }, //设置target为source的位置，大小 clone: function(source, target) { var options = Object.extend({ setLeft: true, setTop: true, setWidth: true, setHeight: true, offsetTop: 0, offsetLeft: 0 }, arguments[2] || {}) // find page position of source source = $(source); var p = Position.page(source); // find coordinate system to use target = $(target); var delta = [0, 0]; var parent = null; // delta [0,0] will do fine with position: fixed elements, // position:absolute needs offsetParent deltas if (Element.getStyle(target,'position') == 'absolute') { parent = Position.offsetParent(target); delta = Position.page(parent); } // correct by body offsets (fixes Safari) if (parent == document.body) { delta[0] -= document.body.offsetLeft; delta[1] -= document.body.offsetTop; } // set position if(options.setLeft) target.style.left = (p[0] - delta[0] + options.offsetLeft) + 'px'; if(options.setTop) target.style.top = (p[1] - delta[1] + options.offsetTop) + 'px'; if(options.setWidth) target.style.width = source.offsetWidth + 'px'; if(options.setHeight) target.style.height = source.offsetHeight + 'px'; }, //将element的position设置为absolute的模式 absolutize: function(element) { element = $(element); if (element.style.position == 'absolute') return; Position.prepare(); var offsets = Position.positionedOffset(element); var top = offsets[1]; var left = offsets[0]; var width = element.clientWidth; var height = element.clientHeight; element._originalLeft = left - parseFloat(element.style.left || 0); element._originalTop = top - parseFloat(element.style.top || 0); element._originalWidth = element.style.width; element._originalHeight = element.style.height; element.style.position = 'absolute'; element.style.top = top + 'px';; element.style.left = left + 'px';; element.style.width = width + 'px';; element.style.height = height + 'px';; }, //将element的position设置为absolute的模式 relativize: function(element) { element = $(element); if (element.style.position == 'relative') return; Position.prepare(); element.style.position = 'relative'; var top = parseFloat(element.style.top || 0) - (element._originalTop || 0); var left = parseFloat(element.style.left || 0) - (element._originalLeft || 0); element.style.top = top + 'px'; element.style.left = left + 'px'; element.style.height = element._originalHeight; element.style.width = element._originalWidth; }} // Safari returns margins on body which is incorrect if the child is absolutely// positioned. For performance reasons, redefine Position.cumulativeOffset for// KHTML/WebKit only.if (/Konqueror|Safari|KHTML/.test(navigator.userAgent)) { Position.cumulativeOffset = function(element) { var valueT = 0, valueL = 0; do { valueT += element.offsetTop || 0; valueL += element.offsetLeft || 0; if (element.offsetParent == document.body) if (Element.getStyle(element, 'position') == 'absolute') break; element = element.offsetParent; } while (element); return [valueL, valueT]; }} 终于把Prototype的所有部分都写完了，哈哈，越来越佩服自己的耐力了下一步决定写写Scriptaculous这个超级流行的效果库

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