zepto源码阅读

  翻完红宝书,第6,7章看完还是似懂非懂,也不想跟着视频写什么高大上的项目,最后想想还是找个简单的JS库看看源码吧。

zepto版本 v1.2.0

代码折叠后的基本结构

//最外层为自执行函数
(function(global, factory) {
if (typeof define === 'function' && define.amd)
//这边是AMD的模块? 不懂,没用过AMD
define(function() { return factory(global) })
else
factory(global)
//为最外层的自执行函数传入this和factory参数
}(this, function(window) {
var Zepto = (function() {
//.....

zepto.Z.prototype = Z.prototype = $.fn

return $
})()
window.Zepto = Zepto //将Zepto赋值给全局Zepto属性
window.$ === undefined && (window.$ = Zepto) //若window.$未被定义,将zepto复制给$

//这边的自执行函数传入Zepto将这个变量作为局部变量,提高效率,缩短使用的作用域链
;(function($){
})(Zepto)

;(function($){
})(Zepto)

;(function($){
})(Zepto)

;(function($){
})(Zepto)

return Zepto
})
)

运行原理

通过自运行函数,将Zepto($)暴露给全局变量Zepto($),此时Zeptp($)为函数,同时该变量下挂载了许多属性方法,通过 $.funName 来调用,当向Zepto($)传入参数后,执行该函数生成对象,同时通过zepto.Z.prototype =Z.prototype = $.fn为生成的对象挂载上DOM的操作方法,部分方法返回值为this(即当前对象),可用于链式操作。

三元运算符“&&”和“||”

源码中使用了很多三元运算符以及赋值问题

操作符||

  1. 只要“||”前面为false,不管“||”后面是true还是false,都返回“||”后面的值。
  2. 只要“||”前面为true,不管“||”后面是true还是false,都返回“||”前面的值。

操作符&&

  1. 只要“&&”前面是false,无论“&&”后面是true还是false,结果都将返“&&”前面的值
  2. 只要“&&”前面是true,无论“&&”后面是true还是false,结果都将返“&&”后面的值

应用

  1. var Yahoo = Yahoo || {}; //赋初值
  2. callback&&callback() //若存在callback则运行callback

执行过程

$ = function(selector, context){
return zepto.init(selector, context)
}
  zepto.init = function(selector, context) {
var dom
//如果传入值空,则返回空对象
if (!selector) return zepto.Z()
//当selector为字符串时
else if (typeof selector == 'string') {
selector = selector.trim()
//判断是否为'<'开头的html标签
if (selector[0] == '<' && fragmentRE.test(selector))
dom = zepto.fragment(selector, RegExp.$1, context), selector = null
// 否则context不为空时,调用 $(context).find(selector)
else if (context !== undefined) return $(context).find(selector)
// 否则则为CSS选择器
else dom = zepto.qsa(document, selector)
}
//如果传入为function
else if (isFunction(selector)) return $(document).ready(selector)
//如果为zepto对象
else if (zepto.isZ(selector)) return selector
else {
//如果传入值为数组是,则除去空数组
if (isArray(selector)) dom = compact(selector)
//如果为对象,则作为DOM数组的成员
else if (isObject(selector))
dom = [selector], selector = null
// 这个是什么意思呢,html传进来不应该在string那边判断么
else if (fragmentRE.test(selector))
dom = zepto.fragment(selector.trim(), RegExp.$1, context), selector = null
// If there's a context, create a collection on that context first, and select
// nodes from there
else if (context !== undefined) return $(context).find(selector)
// And last but no least, if it's a CSS selector, use it to select nodes.
else dom = zepto.qsa(document, selector)
}
// 调用zepto.Z创建对象
return zepto.Z(dom, selector)
}
zepto.Z = function(dom, selector) {
return new Z(dom, selector)
}
function Z(dom, selector) {
var i, len = dom ? dom.length : 0
for (i = 0; i < len; i++) this[i] = dom[i]
this.length = len
this.selector = selector || ''
}

//将$.fn的对象集合赋值给zepto.Z与Z的原型

zepto.Z.prototype = Z.prototype = $.fn

zepto.qsa css选择器

  zepto.qsa = function(element, selector){
var found,
maybeID = selector[0] == '#', //判断是否有ID选择器
maybeClass = !maybeID && selector[0] == '.', //判断是否为Class选择器
nameOnly = maybeID || maybeClass ? selector.slice(1) : selector, // Ensure that a 1 char tag name still gets checked
isSimple = simpleSelectorRE.test(nameOnly) //是否为单选择器
return (element.getElementById && isSimple && maybeID) ? //判断document.getElementByID能否使用
( (found = element.getElementById(nameOnly)) ? [found] : [] ) :
(element.nodeType !== 1 && element.nodeType !== 9 && element.nodeType !== 11) ? [] :
slice.call(
isSimple && !maybeID && element.getElementsByClassName ? // 为单选择器,非id选择器,存在getElementsByClassName
maybeClass ? element.getElementsByClassName(nameOnly) : // 为class选择器
element.getElementsByTagName(selector) : // 否则调用getElementsByTagName
element.querySelectorAll(selector) // 否则调用原生querySelectorAll
)
}

内置方法

isArray

先判断是否有 Array.isArray 方法 否则调用 object instanceof Array

isArray = Array.isArray ||
function(object){ return object instanceof Array }

类型确定方法

  $.each("Boolean Number String Function Array Date RegExp Object Error".split(" "), function(i, name) {
class2type[ "[object " + name + "]" ] = name.toLowerCase()
})

function type(obj) {
return obj == null ? String(obj) :
class2type[toString.call(obj)] || "object"
}
/* 生成 {
'[object boolean]': 'boolean',
'[object number]': 'number',
'[object string]': 'string',
...
} */

类型判断

function isFunction(value) { return type(value) == "function" }

function isWindow(obj) { return obj != null && obj == obj.window }

function isDocument(obj) { return obj != null && obj.nodeType == obj.DOCUMENT_NODE }

function isObject(obj) { return type(obj) == "object" }

function isPlainObject(obj) {
return isObject(obj) && !isWindow(obj) && Object.getPrototypeOf(obj) == Object.prototype
} //判断是否为纯对象 原型与Object的原型一致

function likeArray(obj) {
var length = !!obj && 'length' in obj && obj.length, //对象不为null,存在length属性 则赋值length
type = $.type(obj)

return 'function' != type && !isWindow(obj) && (
'array' == type || length === 0 || // 如果为 array 类型或者length 的值为 0,返回true
(typeof length == 'number' && length > 0 && (length - 1) in obj) // 或者 length 为数字,并且 length的值大于零,并且 length - 1 为 obj 的 key
)
}

其他方法

  //除去数组中为空的元素
function compact(array) { return filter.call(array, function(item){ return item != null }) }
//连接数组
function flatten(array) { return array.length > 0 ? $.fn.concat.apply([], array) : array }
camelize = function(str){ return str.replace(/-+(.)?/g, function(match, chr){ return chr ? chr.toUpperCase() : '' }) }
function dasherize(str) {
return str.replace(/::/g, '/')
.replace(/([A-Z]+)([A-Z][a-z])/g, '$1_$2')
.replace(/([a-z\d])([A-Z])/g, '$1_$2')
.replace(/_/g, '-')
.toLowerCase()
}
//数组去重 除去当前index与第一次出现该项相同的数组项
uniq = function(array){ return filter.call(array, function(item, idx){ return array.indexOf(item) == idx }) }

function classRE(name) {
return name in classCache ?
classCache[name] : (classCache[name] = new RegExp('(^|\\s)' + name + '(\\s|$)'))
}

function maybeAddPx(name, value) {
return (typeof value == "number" && !cssNumber[dasherize(name)]) ? value + "px" : value
}

//在对象中缓存元素节点并默认显示
function defaultDisplay(nodeName) {
var element, display
if (!elementDisplay[nodeName]) {
element = document.createElement(nodeName)
document.body.appendChild(element)
display = getComputedStyle(element, '').getPropertyValue("display")
element.parentNode.removeChild(element)
display == "none" && (display = "block")
elementDisplay[nodeName] = display
}
return elementDisplay[nodeName]
}

function children(element) {
return 'children' in element ?
slice.call(element.children) :
$.map(element.childNodes, function(node){ if (node.nodeType == 1) return node })
}

//生成DOM
zepto.fragment = function(html, name, properties) {
var dom, nodes, container

// 如果为单个html标签
if (singleTagRE.test(html)) dom = $(document.createElement(RegExp.$1))

if (!dom) {
//这边不懂这些正则
if (html.replace) html = html.replace(tagExpanderRE, "<$1></$2>")
if (name === undefined) name = fragmentRE.test(html) && RegExp.$1
if (!(name in containers)) name = '*'

container = containers[name]
container.innerHTML = '' + html
dom = $.each(slice.call(container.childNodes), function(){
container.removeChild(this)
})
}

if (isPlainObject(properties)) {
nodes = $(dom)
$.each(properties, function(key, value) {
if (methodAttributes.indexOf(key) > -1) nodes[key](value)
else nodes.attr(key, value)
})
}

return dom
}

//这俩看不懂
function extend(target, source, deep) {
for (key in source)
if (deep && (isPlainObject(source[key]) || isArray(source[key]))) {
if (isPlainObject(source[key]) && !isPlainObject(target[key]))
target[key] = {}
if (isArray(source[key]) && !isArray(target[key]))
target[key] = []
extend(target[key], source[key], deep)
}
else if (source[key] !== undefined) target[key] = source[key]
}

$.extend = function(target){
var deep, args = slice.call(arguments, 1)
if (typeof target == 'boolean') {
deep = target
target = args.shift()
}
args.forEach(function(arg){ extend(target, arg, deep) })
return target
}

$的工具方法

  $.type = type
$.isFunction = isFunction
$.isWindow = isWindow
$.isArray = isArray
$.isPlainObject = isPlainObject
//判断是否为空对象
$.isEmptyObject = function(obj) {
var name
for (name in obj) return false
return true
}
//判断是否为数字,并且在范围内
$.isNumeric = function(val) {
var num = Number(val), type = typeof val
return val != null && type != 'boolean' &&
(type != 'string' || val.length) &&
!isNaN(num) && isFinite(num) || false
}
//i为起始范围
$.inArray = function(elem, array, i){
return emptyArray.indexOf.call(array, elem, i)
}
//调用内部驼峰转换功能
$.camelCase = camelize
//去除空字符串
$.trim = function(str) {
return str == null ? "" : String.prototype.trim.call(str)
}

$.map = function(elements, callback){
var value, values = [], i, key
//如果为数组
if (likeArray(elements))
for (i = 0; i < elements.length; i++) {
value = callback(elements[i], i)
if (value != null) values.push(value)
}
else //如果为对象
for (key in elements) {
value = callback(elements[key], key)
//为空则跳过
if (value != null) values.push(value)
}
return flatten(values)
}

$.each = function(elements, callback){
var i, key
if (likeArray(elements)) {
for (i = 0; i < elements.length; i++)
//根据返回值停止遍历
if (callback.call(elements[i], i, elements[i]) === false) return elements
} else {
for (key in elements)
if (callback.call(elements[key], key, elements[key]) === false) return elements
}

return elements
}
//调用内部filter方法
$.grep = function(elements, callback){
return filter.call(elements, callback)
}
//根据判断JSON对象方法的存在确定
if (window.JSON) $.parseJSON = JSON.parse

// 生成对象映射数组
$.each("Boolean Number String Function Array Date RegExp Object Error".split(" "), function(i, name) {
class2type[ "[object " + name + "]" ] = name.toLowerCase()
})

$.fn的实例DOM方法

forEach: emptyArray.forEach,
reduce: emptyArray.reduce,
push: emptyArray.push,
sort: emptyArray.sort,
splice: emptyArray.splice,
indexOf: emptyArray.indexOf,
concat: function(){
var i, value, args = []
for (i = 0; i < arguments.length; i++) {
value = arguments[i]
args[i] = zepto.isZ(value) ? value.toArray() : value
}
//将伪数组对象转为数组或连接多个数组项
return concat.apply(zepto.isZ(this) ? this.toArray() : this, args)
},

// 调用工具方法$.map
map: function(fn){
return $($.map(this, function(el, i){ return fn.call(el, i, el) }))
},
slice: function(){
return $(slice.apply(this, arguments))
},

ready: function(callback){
// need to check if document.body exists for IE as that browser reports
// document ready when it hasn't yet created the body element
if (readyRE.test(document.readyState) && document.body) callback($)
else document.addEventListener('DOMContentLoaded', function(){ callback($) }, false)
return this
},
//若传入参数为空,则转换为数组,若非空则返回对应idx值,若为负数则加上length值(与原生方法一致)
get: function(idx){
return idx === undefined ? slice.call(this) : this[idx >= 0 ? idx : idx + this.length]
},
//调用get方法
toArray: function(){ return this.get() },
//返回length属性
size: function(){
return this.length
},
//先判断是否有父节点,有则删除该节点
remove: function(){
return this.each(function(){
if (this.parentNode != null)
this.parentNode.removeChild(this)
})
},
//判断返回值是否为false
each: function(callback){
emptyArray.every.call(this, function(el, idx){
return callback.call(el, idx, el) !== false
})
return this
},
filter: function(selector){
if (isFunction(selector)) return this.not(this.not(selector))
return $(filter.call(this, function(element){
return zepto.matches(element, selector)
}))
},
//添加元素至集合中
add: function(selector,context){
//去除重复元素
return $(uniq(this.concat($(selector,context))))
},
//判断第一个元素是否满足选择器
is: function(selector){
return this.length > 0 && zepto.matches(this[0], selector)
},
not: function(selector){
var nodes=[]
//如果传入参数为方法
if (isFunction(selector) && selector.call !== undefined)
this.each(function(idx){
//传入每个对象
if (!selector.call(this,idx)) nodes.push(this)
})
else {
var excludes = typeof selector == 'string' ? this.filter(selector) :
(likeArray(selector) && isFunction(selector.item)) ? slice.call(selector) : $(selector)
this.forEach(function(el){
if (excludes.indexOf(el) < 0) nodes.push(el)
})
}
return $(nodes)
},
has: function(selector){
return this.filter(function(){
return isObject(selector) ?
//若传入参数为DOM对象
$.contains(this, selector) :
//若传入参数为css选择器
$(this).find(selector).size()
})
},
eq: function(idx){
//若传入为-1 则为最后一个元素,否则为idx,idx+1
return idx === -1 ? this.slice(idx) : this.slice(idx, + idx + 1)
},
first: function(){
//判断是否为对象,并返回第一个元素
var el = this[0]
return el && !isObject(el) ? el : $(el)
},
last: function(){
//判断是否为对象,并返回最后一个元素
var el = this[this.length - 1]
return el && !isObject(el) ? el : $(el)
},
find: function(selector){
var result, $this = this
if (!selector) result = $()
else if (typeof selector == 'object')
result = $(selector).filter(function(){
//若为dom对象通过some过滤出结果
var node = this
return emptyArray.some.call($this, function(parent){
return $.contains(parent, node)
})
})
//如果对象数量为1,则直接从该DOM对象中寻找
else if (this.length == 1) result = $(zepto.qsa(this[0], selector))
else result = this.map(function(){ return zepto.qsa(this, selector) })
return result
},
closest: function(selector, context){
var nodes = [], collection = typeof selector == 'object' && $(selector)
this.each(function(_, node){
while (node && !(collection ? collection.indexOf(node) >= 0 : zepto.matches(node, selector)))
node = node !== context && !isDocument(node) && node.parentNode
if (node && nodes.indexOf(node) < 0) nodes.push(node)
})
return $(nodes)
},
parents: function(selector){
var ancestors = [], nodes = this
while (nodes.length > 0)
//返回元素的所有父元素直到document
nodes = $.map(nodes, function(node){
if ((node = node.parentNode) && !isDocument(node) && ancestors.indexOf(node) < 0) {
ancestors.push(node)
return node
}
})
return filtered(ancestors, selector)
},
parent: function(selector){
return filtered(uniq(this.pluck('parentNode')), selector)
},
children: function(selector){
return filtered(this.map(function(){ return children(this) }), selector)
},
contents: function() {
// 获得每个匹配元素集合元素的子元素,包括文字和注释节点
return this.map(function() { return this.contentDocument || slice.call(this.childNodes) })
},
siblings: function(selector){
//返回除去当前元素的同级元素,若selector存在则过滤
return filtered(this.map(function(i, el){
return filter.call(children(el.parentNode), function(child){ return child!==el })
}), selector)
},
empty: function(){
//清空元素的innerHTML
return this.each(function(){ this.innerHTML = '' })
},
// `pluck` is borrowed from Prototype.js
pluck: function(property){
return $.map(this, function(el){ return el[property] })
},
show: function(){
return this.each(function(){
//若display属性值为none,则去除该属性值
this.style.display == "none" && (this.style.display = '')
//获取该元素最终的CSS属性,使用getPropertyValue方法不必可以驼峰书写形式(不支持驼峰写法
if (getComputedStyle(this, '').getPropertyValue("display") == "none")
this.style.display = defaultDisplay(this.nodeName)
})
},
replaceWith: function(newContent){
//在该元素前插入元素并删除该元素
return this.before(newContent).remove()
},
wrap: function(structure){
var func = isFunction(structure)
if (this[0] && !func)
var dom = $(structure).get(0),
clone = dom.parentNode || this.length > 1

return this.each(function(index){
$(this).wrapAll(
func ? structure.call(this, index) :
clone ? dom.cloneNode(true) : dom
)
})
},
wrapAll: function(structure){
if (this[0]) {
$(this[0]).before(structure = $(structure))
var children
// drill down to the inmost element
while ((children = structure.children()).length) structure = children.first()
$(structure).append(this)
}
return this
},
wrapInner: function(structure){
var func = isFunction(structure)
return this.each(function(index){
var self = $(this), contents = self.contents(),
dom = func ? structure.call(this, index) : structure
contents.length ? contents.wrapAll(dom) : self.append(dom)
})
},
unwrap: function(){
this.parent().each(function(){
$(this).replaceWith($(this).children())
})
return this
},
clone: function(){
return this.map(function(){ return this.cloneNode(true) })
},
hide: function(){
return this.css("display", "none")
},
toggle: function(setting){
return this.each(function(){
var el = $(this)
;(setting === undefined ? el.css("display") == "none" : setting) ? el.show() : el.hide()
})
},
prev: function(selector){ return $(this.pluck('previousElementSibling')).filter(selector || '*') },
next: function(selector){ return $(this.pluck('nextElementSibling')).filter(selector || '*') },
html: function(html){
//若有参数修改innerhtml的值
return 0 in arguments ?
this.each(function(idx){
var originHtml = this.innerHTML
$(this).empty().append( funcArg(this, html, idx, originHtml) )
}) :
//若没参数则直接返回innerHTML值
(0 in this ? this[0].innerHTML : null)
},
//文本内容修改,获取
text: function(text){
return 0 in arguments ?
this.each(function(idx){
var newText = funcArg(this, text, idx, this.textContent)
this.textContent = newText == null ? '' : ''+newText
}) :
(0 in this ? this.pluck('textContent').join("") : null)
},
attr: function(name, value){
var result
//若无第二个参数
return (typeof name == 'string' && !(1 in arguments)) ?
//返回第一个DOM的属性值
(0 in this && this[0].nodeType == 1 && (result = this[0].getAttribute(name)) != null ? result : undefined) :
若有参数,则set属性的值
this.each(function(idx){
if (this.nodeType !== 1) return
if (isObject(name)) for (key in name) setAttribute(this, key, name[key])
else setAttribute(this, name, funcArg(this, value, idx, this.getAttribute(name)))
})
},
removeAttr: function(name){
return this.each(function(){ this.nodeType === 1 && name.split(' ').forEach(function(attribute){
setAttribute(this, attribute)
//这个this是怎么传的?
}, this)})
},
//这个是怎么用的 不懂
prop: function(name, value){
name = propMap[name] || name
return (1 in arguments) ?
this.each(function(idx){
this[name] = funcArg(this, value, idx, this[name])
}) :
(this[0] && this[0][name])
},
//删除DOM节点中的一条属性
removeProp: function(name){
name = propMap[name] || name
return this.each(function(){ delete this[name] })
},
data: function(name, value){
//设置自定义属性data- ,若没有传入属性的值则仅设置属性,返回序列化的data的属性值
var attrName = 'data-' + name.replace(capitalRE, '-$1').toLowerCase()

var data = (1 in arguments) ?
this.attr(attrName, value) :
this.attr(attrName)

return data !== null ? deserializeValue(data) : undefined
},
val: function(value){
// 有参数,设置值
if (0 in arguments) {
if (value == null) value = ""
return this.each(function(idx){
this.value = funcArg(this, value, idx, this.value)
})
} else {
// 如果元素是 <select multiple> 多选列表返回数组
return this[0] && (this[0].multiple ?
$(this[0]).find('option').filter(function(){ return this.selected }).pluck('value') :
this[0].value)
}
},
offset: function(coordinates){
//如果参数存在,则设置对应的属性
if (coordinates) return this.each(function(index){
var $this = $(this),
coords = funcArg(this, coordinates, index, $this.offset()),
parentOffset = $this.offsetParent().offset(),
props = {
top: coords.top - parentOffset.top,
left: coords.left - parentOffset.left
}
//如果属性为static则改为relaticv并赋值
if ($this.css('position') == 'static') props['position'] = 'relative'
$this.css(props)
})
if (!this.length) return null
if (document.documentElement !== this[0] && !$.contains(document.documentElement, this[0]))
return {top: 0, left: 0}
var obj = this[0].getBoundingClientRect()
return {
left: obj.left + window.pageXOffset,
top: obj.top + window.pageYOffset,
width: Math.round(obj.width),
height: Math.round(obj.height)
}
},
css: function(property, value){
if (arguments.length < 2) {
//获取第一个元素
var element = this[0]
//如果属性为字符串,则修改css的值
if (typeof property == 'string') {
if (!element) return
return element.style[camelize(property)] || getComputedStyle(element, '').getPropertyValue(property)
//如果属性为数组,则返回对应的属性值
} else if (isArray(property)) {
if (!element) return
var props = {}
var computedStyle = getComputedStyle(element, '')
$.each(property, function(_, prop){
props[prop] = (element.style[camelize(prop)] || computedStyle.getPropertyValue(prop))
})
return props
}
}

var css = ''
// 其他情况:有两个参数、property是对象
if (type(property) == 'string') {
// property 是字符串,设置单个样式
if (!value && value !== 0)
this.each(function(){ this.style.removeProperty(dasherize(property)) })
else
css = dasherize(property) + ":" + maybeAddPx(property, value)
} else {
for (key in property)
//property 是对象,若属性值为空或未定义,则删除属性
if (!property[key] && property[key] !== 0)
this.each(function(){ this.style.removeProperty(dasherize(key)) })
else
css += dasherize(key) + ':' + maybeAddPx(key, property[key]) + ';'
}
//通过cssText修改CSS
return this.each(function(){ this.style.cssText += ';' + css })
},
index: function(element){
//有参数则返回该dom的index,否则返回该dom在兄弟元素中的index
return element ? this.indexOf($(element)[0]) : this.parent().children().indexOf(this[0])
},
hasClass: function(name){
//判断是否有某一css属性
if (!name) return false
return emptyArray.some.call(this, function(el){
return this.test(className(el))
}, classRE(name))
},
addClass: function(name){
if (!name) return this
return this.each(function(idx){
//判断是否存在className属性
if (!('className' in this)) return
classList = []
//保留原来的class
var cls = className(this), newName = funcArg(this, name, idx, cls)
//数组中存入不存在的class
newName.split(/\s+/g).forEach(function(klass){
if (!$(this).hasClass(klass)) classList.push(klass)
}, this)
//传入className
classList.length && className(this, cls + (cls ? " " : "") + classList.join(" "))
})
},
removeClass: function(name){
return this.each(function(idx){
//判断是否存在className属性
if (!('className' in this)) return
if (name === undefined) return className(this, '')
classList = className(this)
funcArg(this, name, idx, classList).split(/\s+/g).forEach(function(klass){
//将匹配的cssName替换为空
classList = classList.replace(classRE(klass), " ")
})
//赋值cssName
className(this, classList.trim())
})
},
toggleClass: function(name, when){
if (!name) return this
return this.each(function(idx){
var $this = $(this), names = funcArg(this, name, idx, className(this))
names.split(/\s+/g).forEach(function(klass){
// 如果有 when 参数,则只通过when参数判断,true则只执行addClass,false则只执行removeClass
// 如果没有 when 参数,则判断元素有没有该class,有则移除,没有则添加
(when === undefined ? !$this.hasClass(klass) : when) ?
$this.addClass(klass) : $this.removeClass(klass)
})
})
},
scrollTop: function(value){
if (!this.length) return
var hasScrollTop = 'scrollTop' in this[0]
//如果无参数,直接返回属性值
if (value === undefined) return hasScrollTop ? this[0].scrollTop : this[0].pageYOffset
return this.each(hasScrollTop ?
function(){ this.scrollTop = value } :
function(){ this.scrollTo(this.scrollX, value) })
},
scrollLeft: function(value){
//同上
if (!this.length) return
var hasScrollLeft = 'scrollLeft' in this[0]
if (value === undefined) return hasScrollLeft ? this[0].scrollLeft : this[0].pageXOffset
return this.each(hasScrollLeft ?
function(){ this.scrollLeft = value } :
function(){ this.scrollTo(value, this.scrollY) })
},
position: function() {
if (!this.length) return

var elem = this[0],
// 找到第一个定位过的祖先元素 “relative”, “absolute” or “fixed”
offsetParent = this.offsetParent(),
// 获取当前偏移
offset = this.offset(),
parentOffset = rootNodeRE.test(offsetParent[0].nodeName) ? { top: 0, left: 0 } : offsetParent.offset()

// 去掉当前元素的 margin 宽度
// note: when an element has margin: auto the offsetLeft and marginLeft
// are the same in Safari causing offset.left to incorrectly be 0
offset.top -= parseFloat( $(elem).css('margin-top') ) || 0
offset.left -= parseFloat( $(elem).css('margin-left') ) || 0

// 增加父元素的 border 宽度
parentOffset.top += parseFloat( $(offsetParent[0]).css('border-top-width') ) || 0
parentOffset.left += parseFloat( $(offsetParent[0]).css('border-left-width') ) || 0

// Subtract the two offsets
return {
top: offset.top - parentOffset.top,
left: offset.left - parentOffset.left
}
},
offsetParent: function() {
return this.map(function(){
var parent = this.offsetParent || document.body
// 如果获取的parent不是null、不是body或html、而且position==static,继续查找,直到为根元素
while (parent && !rootNodeRE.test(parent.nodeName) && $(parent).css("position") == "static")
parent = parent.offsetParent
return parent
})
}