javascript与CSS复习（《精通javascript》）

//get a style property (name) of a specific element (elem)
function getStyle(elem, name) {
　　// if the property exists in style[], then it's been set
　　//recently (and is current)
if(elem.style[name]) return elem.style[name];
//otherwise, try to use IE's method
else if (elem.currentStyle) return elem.currentStyle[name];
//Or the W3C's method, if it exists
else if (document.defaultView && document.defaultView.getComputedStyle) {
　　　　　　//it uses the traditional 'text-align' style of rule writing
　　　　　　//instead of textAlign
name = name.replace(/[A-Z]/g, '-$1');
name = name.toLowerCase();
//get the style object and get the value of the property ( if it exists)
　　　　　　var s = document.defaultView.getComputedStyle(elem,'');
return s && s.getPropertyValue(name);
　　} else return null;
}

//find the x (horizontal, Left) position of an element
function pageX(elem) {
　　//see if we're at the root element, or not
return elem.offsetParent ?
//if we can still go up, add the current offset and recurse upwards
　　　　　　elem.offsetLeft + pageX(elem.offsetParent) :
　　　　　　//otherwise, just get the current offset
　　　　　　elem.offsetLeft;
}
//find the y (vertical, top) position of an element
function pageY(elem) {
　　//see if we're at the root element, or not
　　return elem.offsetParent ?
//if we can still go up, add the current offset and recurse upwards
　　 elem.offsetTop + pageY(elem.offsetParent) :
//otherwise, just get the current offset
elem.offsetTop;
}

//find the horizontal position of an element within its parent
function parentX(elem) {
　　//if the offsetParent is the element's parent, break early
　　return elem.parentNode == elem.offsetParent ?
elem.offsetLeft :
// otherwise, we need to find the position relative to the entire
// page for both elements, and find the difference
pageX(elem) - pageX(elem.parentNode);
}
//find the vertical positioning of an element within its parent
function parentY(elem) {
　　//if the offsetParent is the element's parent, break early
return elem.parentNode == elem.offsetParent ?
　　　　elem.offsetTop :
// otherwise, we need to find the position relative to the entire
// page for both elements, and find the difference
pageY(elem) - pageY(elem.parentNode);
}

//find the left position of an element
function posX(elem) {
　　//get the computed style and get the number out of the value
return parseInt(getStyle(elem, 'left'));
}
//find the top position of an element
function posY(elem) {
　　//get the computed style and get the number out of the value
return parseInt(getStyle(elem, 'top'));
}

//a function for setting the horizontal position of an element
function setX(elem, pos) {
　　//set the 'left' css property, using pixel units
　　elem.style.left = pos + 'px';
}
//a function for setting the vertical position of an element
function setY(elem, pos) {
　　//set the 'top' css property, using pixel units
　　elem.style.top = pos + 'px';
}

//a function for adding a number of pixels to the horizontal
//position of an element
function addX(elem, pos) {
　　//get the current horz. position and add the offset to it
setX(elem, posX(elem) + pos);
}
//a function that can be used to add a number of pixels to the
//vertical position of an element
function addY(elem, pos) {
　　//get the current vertical position and add the offset to it
setY(elem, posY(elem) + pos);
}

function getHeight(elem) {
　　return parseInt(getStyle(elem, 'height'));
}
function getWidth(elem) {
　　return parseInt(getStyle(elem, 'width'));
}

//查找元素完整的、可能的高度
function fullHeight(elem) {
　　//如果元素是显示的，那么使用offsetHeight就能得到高度，如果没有offsetHeight，则使用getHeight()
　　if(getStyle(elem, 'display') != 'none')
　　　　　　return elem.offsetHeight || getHeight(elem);
//否则，我们必须处理display为none的元素，所以重置它的css属性以获得更精确的读数
var old = resetCSS(elem, {
　　display:'',
visibility:'hidden',
position:'absolute'
});
//使用clientHeigh找出元素的完整高度，如果还不生效，则使用getHeight函数
var h = elem.clientHeight || getHeight(elem);
//最后，恢复其css的原有属性
restoreCSS(elem, old);
//并返回元素的完整高度
return h;
}
//查找元素完整的、可能的宽度
function fullWidth(elem) {
　　//如果元素是显示的，那么使用offsetWidth就能得到宽度，如果没有offsetWidth,则使用getWidth()
if(getStyle(elem, 'display') != 'none')
　　　　return elem.offsetWidth || getWidth(elem);
//否则，我们必须处理display为none的元素，所以重置它的css以获取更精确的读数
var old = resetCSS(elem, {
　　　display:'',
visibility:'hidden',
position:'absolute'
});
//使用clientWidth找出元素的完整高度，如果还不生效，则使用getWidth函数
var w = elem.clientWidth || getWidth(elem);
//最后，恢复原有CSS
　restoreCSS(elem, old);
//返回元素的完整宽度
return w;
}
//设置一组CSS属性的函数
function resetCSS(elem, prop) {
　　var old = {};
//遍历每个属性
for(var i in prop) {
　　//记录旧的属性值
old[i] = elem.style[i];
　　　　//设置新的值
　　　　elem.style[i] = prop[i];
}
return old;
}
//恢复原有CSS属性
function restoreCSS(elem, prop) {
　　for(var i in prop)
　　　　elem.style[i] = prop[i];
}