Position是prototype中定義的一個(gè)對(duì)象，提供了操作DOM中與位置相關(guān)的方法，要很好的理解元素在頁(yè)面中的位置，可以參考這篇文章：Relatively Absolute
具體代碼如下，按照代碼說(shuō)說(shuō)，其中英文是作者的注釋?zhuān)形募t色的才是偶的說(shuō)明或翻譯英文的注釋?zhuān)捎庙斒阶⑨尫?注釋在要說(shuō)明的代碼的上面)說(shuō)明
// set to true if needed, warning: firefox performance problems
// NOT neeeded for page scrolling, only if draggable contained in
// scrollable elements
//只有在使用拖動(dòng)的時(shí)候元素包含在有滾動(dòng)條的元素中才需要設(shè)置為true
includeScrollOffsets: false,
// must be called before calling withinIncludingScrolloffset, every time the
// page is scrolled
//當(dāng)頁(yè)面被scrolled后，使用withinIncludingScrolloffset的時(shí)候需要先調(diào)用這個(gè)方法
prepare: function() {
//橫向滾動(dòng)條滾動(dòng)的距離
this.deltaX = window.pageXOffset
|| document.documentElement.scrollLeft
|| document.body.scrollLeft
|| 0;
//縱向滾動(dòng)條滾動(dòng)的距離
this.deltaY = window.pageYOffset
|| document.documentElement.scrollTop
|| document.body.scrollTop
|| 0;
},
//元素由于滾動(dòng)條偏移的總距離
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];
},
//元素在頁(yè)面中由offsetParent累積的offset，當(dāng)offsetParent都沒(méi)有滾動(dòng)條時(shí)，就是元素在頁(yè)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];
},
//元素相對(duì)于containing block("nearest positioned ancestor")的位置，也就是相對(duì)于最近的一個(gè)position設(shè)置為relative或者absolute的祖先節(jié)點(diǎn)的位置，如果沒(méi)有就是相對(duì)于body的位置，跟style.top，style.left一樣？
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
//判斷指定的位置是否在元素內(nèi)
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，不過(guò)考慮到滾動(dòng)條，也許是在元素上面，但不是直接在上面，因?yàn)闈L動(dòng)條也許已經(jīng)使元素不可見(jiàn)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
//在調(diào)用這個(gè)方法前，必須先調(diào)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;
},
//返回元素相對(duì)頁(yè)面的真實(shí)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];
},
//設(shè)置target為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';
},
//將element的position設(shè)置為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';;
},
//將element的position設(shè)置為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];
}
}
終于把Prototype的所有部分都寫(xiě)完了，哈哈，越來(lái)越佩服自己的耐力了
下一步?jīng)Q定寫(xiě)寫(xiě)Scriptaculous這個(gè)超級(jí)流行的效果庫(kù)
