Tooltip插件可以让你把要显示的内容以弹出框的形式来展示，如：

因为自己在工作的过程中，用到了Tooltip这个插件，并且当时正想学习一下元素定位的问题，如：提示框显示的位置就是触发提示框元素的位置，可以配置在上、下、左、右等位置，所以就去看了源码。对于整个插件源码没有看全，但也学到了许多的知识点。能力有限，可能其中有认识错误的地方，以后再补充吧

1 使用方法不介绍 ，可以参照

2 源码解析

+function ($) {
 'use strict';
 // TOOLTIP PUBLIC CLASS DEFINITION
 // ===============================

 this.$viewport = this.options.viewport $(this.options.viewport.selector || this.options.viewport)
 //多个触发器 即触发函数
 var triggers = this.options.trigger.split(' ')

 //触发时执行$.proxy(this.toggle, this)返回的函数
 this.$element.on('click.' + this.type, this.options.selector, $.proxy(this.toggle, this))
 } else if (trigger != 'manual') {
 var eventIn = trigger == 'hover' 'mouseenter' : 'focusin'
 var eventOut = trigger == 'hover' 'mouseleave' : 'focusout'
 this.$element.on(eventIn + '.' + this.type, this.options.selector, $.proxy(this.enter, this))
 this.$element.on(eventOut + '.' + this.type, this.options.selector, $.proxy(this.leave, this))
 this.options.selector 
 (this._options = $.extend({}, this.options, { trigger: 'manual', selector: '' })) :
 this.fixTitle()
 Tooltip.prototype.getDefaults = function () {
 return Tooltip.DEFAULTS
 //获得初始化参数
 Tooltip.prototype.getOptions = function (options) {
 // this.$element.data() data-key = value 形式的属性获取 
 // 返回一个对象{key:value}
 // options 元素属性 默认 
 options = $.extend({}, this.getDefaults(), this.$element.data(), options)
 //delay 为数字 特殊处理
 //delay 为对象 delay:{ show: 500, hide: 100 }
 if (options.delay typeof options.delay == 'number') {
 options.delay = {
 show: options.delay,
 hide: options.delay
 return options
 Tooltip.prototype.getDelegateOptions = function () {
 var options = {}
 var defaults = this.getDefaults()
 this._options $.each(this._options, function (key, value) {
 if (defaults[key] != value) options[key] = value
 return options
 //提示框显示
 Tooltip.prototype.enter = function (obj) {
 //obj是否是tooltip的实例
 var self = obj instanceof this.constructor 
 obj : $(obj.currentTarget).data('bs.' + this.type)
 //$tip.is(':visible') 该div是否可见
 //可见时 只更新状态 然后直接返回
 if (self self.$tip self.$tip.is(':visible')) {
 self.hoverState = 'in'
 return
 //self 不存在
 if (!self) {
 self = new this.constructor(obj.currentTarget, this.getDelegateOptions())
 $(obj.currentTarget).data('bs.' + this.type, self)
 //上次点击延时未显示 则取消显示
 clearTimeout(self.timeout)
 //设置状态
 self.hoverState = 'in'
 //delay: 数字 (默认 0) 或 对象 { show: 500, hide: 100 }
 //没有delay delay.show 时 直接显示 
 if (!self.options.delay || !self.options.delay.show) return self.show()
 //延时显示 self.options.delay.show:延时时间
 self.timeout = setTimeout(function () {
 if (self.hoverState == 'in') self.show()
 }, self.options.delay.show)
 //提示框隐藏
 Tooltip.prototype.leave = function (obj) {
 var self = obj instanceof this.constructor 
 obj : $(obj.currentTarget).data('bs.' + this.type)
 if (!self) {
 self = new this.constructor(obj.currentTarget, this.getDelegateOptions())
 $(obj.currentTarget).data('bs.' + this.type, self)
 clearTimeout(self.timeout)
 self.hoverState = 'out'
 if (!self.options.delay || !self.options.delay.hide) return self.hide()
 self.timeout = setTimeout(function () {
 if (self.hoverState == 'out') self.hide()
 }, self.options.delay.hide)
 //提示框显示核心方法
 Tooltip.prototype.show = function () {
 (this) 
 var e = $.Event('show.bs.' + this.type)
 if (this.hasContent() this.enabled) {
 this.$element.trigger(e)
 //判断是否在根节点中
 //this.$element[0] 转换为DOM对象
 //.ownerDocument Document文档对象
 //.documentElement 根节点 HTML标签
 //$.contains 一个DOM节点是否包含另一个DOM节点。
 var inDom = $.contains(this.$element[0].ownerDocument.documentElement, this.$element[0])
 //调用preventDefault 或 不在根节点 return
 //事件对象中是否调用过 event.preventDefault()
 //event.preventDefault():阻止元素发生默认的行为
 //如 当点击提交按钮时阻止对表单的提交 、 阻止以下 URL 的链接
 if (e.isDefaultPrevented() || !inDom) return
 var that = this
 var $tip = this.tip()
 var tipId = this.getUID(this.type)
 //设置提示框的title
 this.setContent()
 $tip.attr('id', tipId)
 this.$element.attr('aria-describedby', tipId)
 //参数animation
 if (this.options.animation) $tip.addClass('fade')
 //参数placement 提示框的位置 top bottom left right
 var placement = typeof this.options.placement == 'function' 
 this.options.placement.call(this, $tip[0], this.$element[0]) :
 this.options.placement
 // 判断placement是否包含"auto"
 var autoToken = /\s auto \s /i
 var autoPlace = autoToken.test(placement)
 //包含 "auto"时
 if (autoPlace) placement = placement.replace(autoToken, '') || 'top'
 $tip
 //detach() 删除匹配的对象 与remove()不同的是，所有绑定的事件、附加的数据等都会保留下来
 .detach()
 .css({ top: 0, left: 0, display: 'block' })
 .addClass(placement)
 .data('bs.' + this.type, this)
 //参数 container 向指定元素添加该提示框
 //没有 添加到当前元素后面
 this.options.container $tip.appendTo(this.options.container) : $tip.insertAfter(this.$element)
 //位置对象pos pos = {top: , right: , bottom: , left: , width: ,scroll:}
 var pos = this.getPosition()
 //提示框自身实际的 width height
 var actualWidth = $tip[0].offsetWidth
 var actualHeight = $tip[0].offsetHeight
 if (autoPlace) {
 Placement = placement
 var $container = this.options.container $(this.options.container) : this.$element.parent()
 var containerDim = this.getPosition($container)
 placement = placement == 'bottom' pos.bottom + actualHeight containerDim.bottom 'top' :
 placement == 'top' pos.top - actualHeight containerDim.top 'bottom' :
 placement == 'right' pos.right + actualWidth containerDim.width 'left' :
 placement == 'left' pos.left - actualWidth containerDim.left 'right' :
 placement
 $tip
 .Placement)
 .addClass(placement)
 //计算提示框的偏移量 {top: , left: }
 var calculatedOffset = this.getCalculatedOffset(placement, pos, actualWidth, actualHeight)
 //应用并设置偏移量
 this.applyPlacement(calculatedOffset, placement)
 plete = function () {
 var prevHoverState = that.hoverState
 that.$element.trigger('shown.bs.' + that.type)
 that.hoverState = null
 if (prevHoverState == 'out') that.leave(that)
 $.support.transition this.$tip.hasClass('fade') 
 $tip
 .one('bsTransitionEnd', complete)
 .emulateTransitionEnd(Tooltip.TRANSITION_DURATION) :
 complete()
 Tooltip.prototype.applyPlacement = function (offset, placement) {
 var $tip = this.tip()
 var width = $tip[0].offsetWidth
 var height = $tip[0].offsetHeight
 // manually read margins because getBoundingClientRect includes difference
 //获得提示框自身的外边距的值
 var marginTop = parseInt($tip.css('margin-top'), 10)
 var marginLeft = parseInt($tip.css('margin-left'), 10)
 // we must check for NaN for ie 8/9
 //是否是非数字
 if (isNaN(marginTop)) marginTop = 0
 if (isNaN(marginLeft)) marginLeft = 0
 //计算的偏移量 + 自身的外边距
 offset.top = offset.top + marginTop
 offset.left = offset.left + marginLeft
 // $.fn.offset doesn't round pixel values
 // so we use setOffset directly with our own function B-0
 // 应用了offset.setOffset方法，传入了using参数，因为offset设置值的时候，不能四舍五入
 $.offset.setOffset($tip[0], $.extend({
 using: function (pro凡科抠图) {
 $tip.css({
 top: Math.round(pro凡科抠图.top),
 left: Math.round(pro凡科抠图.left)
 }, offset), 0)
 //添加 in class 让提示框显示
 $tip.addClass('in')
 // check to see if placing tip in new offset caused the tip to resize itself
 //获取显示后的提示框的宽和高 检查是否调整了自身的大小
 var actualWidth = $tip[0].offsetWidth
 var actualHeight = $tip[0].offsetHeight

 if (placement == 'top' actualHeight != height) {
 offset.top = offset.top + height - actualHeight
 var delta = this.getViewportAdjustedDelta(placement, offset, actualWidth, actualHeight)
 if (delta.left) offset.left += delta.left
 else offset.top += delta.top
 var isVertical = /top|bottom/.test(placement)
 var arrowDelta = isVertical delta.left * 2 - width + actualWidth : delta.top * 2 - height + actualHeight
 var arrowOffsetPosition = isVertical 'offsetWidth' : 'offsetHeight'
 $tip.offset(offset)
 this.replaceArrow(arrowDelta, $tip[0][arrowOffsetPosition], isVertical)
 Tooltip.prototype.replaceArrow = function (delta, dimension, isHorizontal) {
 this.arrow()
 .css(isHorizontal 'left' : 'top', 50 * (1 - delta / dimension) + '%')
 .css(isHorizontal 'top' : 'left', '')
 //设置提示框的title
 Tooltip.prototype.setContent = function () {
 //div
 var $tip = this.tip()
 var title = this.getTitle()
 $ 'html' : 'text'](title)
 $tip.removeClass('fade in top bottom left right')
 Tooltip.prototype.hide = function (callback) {
 var that = this
 var $tip = this.tip()
 var e = $.Event('hide.bs.' + this.type)
 plete() {
 if (that.hoverState != 'in') $tip.detach()
 that.$element
 .removeAttr('aria-describedby')
 .trigger('hidden.bs.' + that.type)
 callback callback()
 this.$element.trigger(e)
 if (e.isDefaultPrevented()) return
 $tip.removeClass('in')
 $.support.transition this.$tip.hasClass('fade') 
 $tip
 .one('bsTransitionEnd', complete)
 .emulateTransitionEnd(Tooltip.TRANSITION_DURATION) :
 complete()
 this.hoverState = null
 return this
 Tooltip.prototype.fixTitle = function () {
 var $e = this.$element
 if ($e.attr('title') || typeof ($e.attr('data-original-title')) != 'string') {
 $e.attr('data-original-title', $e.attr('title') || '').attr('title', '')
 Tooltip.prototype.hasContent = function () {
 return this.getTitle()
 //获取位置
 Tooltip.prototype.getPosition = function ($element) {
 //不传入 则为当前点击元素
 $element = $element || this.$element
 //转换为DOM对象
 var el = $element[0]
 //是否是body元素
 var isBody = el.tagName == 'BODY'
 //获取元素各边与页面上边和左边的距离 left right top bottom height width
 var elRect = el.getBoundingClientRect()
 //兼容IE8 没有 width height 则计算
 if (elRect.width == null) {
 // width and height are missing in IE8, so compute them manually; see twbs/bootstrap/issues/14093
 elRect = $.extend({}, elRect, { width: elRect.right - elRect.left, height: elRect.bottom - elRect.top })
 //当前元素相对于文档的偏移量
 var elOffset = isBody { top: 0, left: 0 } : $element.offset()
 //垂直滚动条的距离
 //document.documentElement.scrollTop 和 document.body.scrollTop 浏览器兼容 
 var scroll = { scroll: isBody document.documentElement.scrollTop || document.body.scrollTop : $element.scrollTop() }
 var outerDims = isBody { width: $(window).width(), height: $(window).height() } : null
 //合并 
 return $.extend({}, elRect, scroll, outerDims, elOffset)
 //计算偏移量
 Tooltip.prototype.getCalculatedOffset = function (placement, pos, actualWidth, actualHeight) {
 return placement == 'bottom' { top: pos.top + pos.height, left: pos.left + pos.width / 2 - actualWidth / 2 } :
 placement == 'top' { top: pos.top - actualHeight, left: pos.left + pos.width / 2 - actualWidth / 2 } :
 placement == 'left' { top: pos.top + pos.height / 2 - actualHeight / 2, left: pos.left - actualWidth } :
 /* placement == 'right' */ { top: pos.top + pos.height / 2 - actualHeight / 2, left: pos.left + pos.width }

 Tooltip.prototype.getViewportAdjustedDelta = function (placement, pos, actualWidth, actualHeight) {
 var delta = { top: 0, left: 0 }
 //默认参数
 //viewport: {
 // selector: 'body',
 // padding: 0
 //默认的话 this.$viewport = 'body'
 if (!this.$viewport) return delta
 var viewportPadding = this.options.viewport this.options.viewport.padding || 0
 //this.$viewport = 'body' width height为 window的
 var viewportDimensions = this.getPosition(this.$viewport)
 (viewportDimensions)
 if (/right|left/.test(placement)) {
 var topEdgeOffset = pos.top - viewportPadding - viewportDimensions.scroll
 var bottomEdgeOffset = pos.top + viewportPadding - viewportDimensions.scroll + actualHeight
 if (topEdgeOffset viewportDimensions.top) { // top overflow
 delta.top = viewportDimensions.top - topEdgeOffset
 } else if (bottomEdgeOffset viewportDimensions.top + viewportDimensions.height) { // bottom overflow
 delta.top = viewportDimensions.top + viewportDimensions.height - bottomEdgeOffset
 } else {
 var leftEdgeOffset = pos.left - viewportPadding
 var rightEdgeOffset = pos.left + viewportPadding + actualWidth
 if (leftEdgeOffset viewportDimensions.left) { // left overflow
 delta.left = viewportDimensions.left - leftEdgeOffset
 } else if (rightEdgeOffset viewportDimensions.width) { // right overflow
 delta.left = viewportDimensions.left + viewportDimensions.width - rightEdgeOffset
 return delta
 //提示框的title
 Tooltip.prototype.getTitle = function () {
 var title
 var $e = this.$element
 var o = this.options
 //先获取当前元素的data-original-title属性
 //否则获取参数title
 title = $e.attr('data-original-title')
 || (typeof o.title == 'function' o.title.call($e[0]) : o.title)
 return title
 //随机生成唯一id 0 -- 100000 id值 
 Tooltip.prototype.getUID = function (prefix) {
 //~~ 去掉小数部分
 do prefix += ~~(Math.random() * 1000000)
 while (document.getElementById(prefix))
 return prefix
 //生成提示框的div
 //不存在 则用模板
 // div role="tooltip" div /div div /div /div 
 Tooltip.prototype.tip = function () {
 return (this.$tip = this.$tip || $(this.options.template))
 Tooltip.prototype.arrow = function () {
 return (this.$arrow = this.$arrow || this.tip().find('.tooltip-arrow'))
 Tooltip.prototype.enable = function () {
 this.enabled = true
 Tooltip.prototype.disable = function () {
 this.enabled = false
 Tooltip.prototype.toggleEnabled = function () {
 this.enabled = !this.enabled
 //click 事件触发时执行的函数
 Tooltip.prototype.toggle = function (e) {
 //this tooltip实例对象
 var self = this
 if (e) {
 //e.currentTarget 返回注册该事件处理程序的元素
 self = $(e.currentTarget).data('bs.' + this.type)
 if (!self) {
 self = new this.constructor(e.currentTarget, this.getDelegateOptions())
 $(e.currentTarget).data('bs.' + this.type, self)
 //判断提示框当前的状态
 //true 当前显示 需要隐藏
 //false 相反
 self.tip().hasClass('in') self.leave(self) : self.enter(self)
 Tooltip.prototype.destroy = function () {
 var that = this
 clearTimeout(this.timeout)
 this.hide(function () {
 that.$element.off('.' + that.type).removeData('bs.' + that.type)

 //option为字符串 则是方法 options:false 
 var options = typeof option == 'object' option
 //option是对象 执行初始化 ，并提供了选择器
 var selector = options options.selector
 //是destroy 方法 不执行
 if (!data option == 'destroy') return
 //tooltip初始化
 if (selector) {
 //存在选择器，则将当前点击元素 bs.tooltip = {} 即去掉Tooltip实例
 if (!data) $this.data('bs.tooltip', (data = {}))
 //给选择器加上Tooltip实例
 if (!data[selector]) data[selector] = new Tooltip(this, options)
 } else {
 //没有value值时，则加上 bs.tooltip = data(new Tooltip(this, options)) 
 if (!data) $this.data('bs.tooltip', (data = new Tooltip(this, options)))
 //执行方法
 if (typeof option == 'string') data[option]()
 //缓存以前$.fn上的tooltip
 var old = $.fn.tooltip
 //添加到jQuery对象上
 $.fn.tooltip = Plugin
 $.fn.tooltip.Constructor = Tooltip

 //var other = $("#aa").tooltip().noConflict();
 $.fn.tooltip.noConflict = function () {
 $.fn.tooltip = old
 return this
}(jQuery);

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持凡科。