zepto 事件模块源码分析

//     Zepto.js
//     (c) 2010-2016 Thomas Fuchs
//     Zepto.js may be freely distributed under the MIT license.

;(function($){
  //_zid:element的唯一标识
  var _zid = 1, undefined,   
      slice = Array.prototype.slice,
      isFunction = $.isFunction,
      isString = function(obj){ return typeof obj == 'string' },
      handlers = {},
      specialEvents={},
      //focusin focusout不是所有浏览器都支持的。谷歌支持，IE从10开始支持，火狐一直不支持
      //https://developer.mozilla.org/en-US/docs/Web/Events 此处可以看出focus blur不支持冒泡.在支持的浏览器中，顺序如下focus>>focusin>>blur>>focusout
      focusinSupported = 'onfocusin' in window,
      focus = { focus: 'focusin', blur: 'focusout' },
      //https://developer.mozilla.org/en-US/docs/Web/Events/mouseenter mouseenter不冒泡 mouseover冒泡。这就会导致父节点监听mouseover事件，其子节点有mouseover时，父节点一回收到mouseover事件
      hover = { mouseenter: 'mouseover', mouseleave: 'mouseout' }

  specialEvents.click = specialEvents.mousedown = specialEvents.mouseup = specialEvents.mousemove = 'MouseEvents' //一般事件用Events

  function zid(element) {
    return element._zid || (element._zid = _zid++)
  }
  
  /*
  查找一个预算绑定的函数 事件类型相同，命名空间相同 选择器相同
  输入节点，事件类型  
  输出处理函数
  */
  function findHandlers(element, event, fn, selector) {
    event = parse(event)
    if (event.ns) var matcher = matcherFor(event.ns)
    return (handlers[zid(element)] || []).filter(function(handler) {
      return handler
        && (!event.e  || handler.e == event.e)
        && (!event.ns || matcher.test(handler.ns))
        && (!fn       || zid(handler.fn) === zid(fn))
        && (!selector || handler.sel == selector)
    })
  }
  
  //解析事件类型、命名空间
  function parse(event) {
    var parts = ('' + event).split('.')
    return {e: parts[0], ns: parts.slice(1).sort().join(' ')}
  }
  function matcherFor(ns) {
    return new RegExp('(?:^| )' + ns.replace(' ', ' .* ?') + '(?: |$)')
  }

  //对于不冒泡的事件要用捕获的方法达到冒泡的目的
  function eventCapture(handler, captureSetting) {
    return handler.del &&
      (!focusinSupported && (handler.e in focus)) ||
      !!captureSetting
  }

  //将不可冒泡的事件用可冒泡的事件代替
  function realEvent(type) {
    return hover[type] || (focusinSupported && focus[type]) || type
  }

  //核心函数
  function add(element, events, fn, data, selector, delegator, capture){
    //set是该节点绑定的监听函数集合
    var id = zid(element), set = (handlers[id] || (handlers[id] = []))
    events.split(/s/).forEach(function(event){
      if (event == 'ready') return $(document).ready(fn)
      var handler   = parse(event)
      handler.fn    = fn
      handler.sel   = selector
      // emulate mouseenter, mouseleave
      
      if (handler.e in hover) fn = function(e){
        /*
          event有：target：事件发生的节点  currentTarget:监听器所在的节点 relatedTarget:只对mouseover mouseenter mouseout一类事件有效。进入一个节点，被进入的是target，从哪进入的是relatedTarget
          下面的判断的意思是：若不是内部移动，则执行函数。可以避免收到多次mouseenter、mouseleave事件
        */
        var related = e.relatedTarget
        if (!related || (related !== this && !$.contains(this, related)))
          return handler.fn.apply(this, arguments)
      }
      handler.del   = delegator
      var callback  = delegator || fn
      //事件处理函数 加一层代理 方便删除，并加入preventDefault() stopPropagation()
      handler.proxy = function(e){
        e = compatible(e)
        if (e.isImmediatePropagationStopped()) return  //若事件某一步已执行了stopImmediatePropagationStop()，则回调函数不再执行（从源节点到各个接收到冒泡事件的父节点都是同一个事件）
        e.data = data
        var result = callback.apply(element, e._args == undefined ? [e] : [e].concat(e._args))
        if (result === false) e.preventDefault(), e.stopPropagation() //回调函数 返回false，则不再冒泡或执行默认事件
        return result
      }
      handler.i = set.length
      set.push(handler)
      if ('addEventListener' in element)
        element.addEventListener(realEvent(handler.e), handler.proxy, eventCapture(handler, capture)) //eventCapture保证绑定在父节点上的监听函数可以收到事件，避免不冒泡的事件导致父节点监听不到的情况
    })
  }
  function remove(element, events, fn, selector, capture){
    var id = zid(element)
    ;(events || '').split(/s/).forEach(function(event){
      findHandlers(element, event, fn, selector).forEach(function(handler){
        delete handlers[id][handler.i]
      if ('removeEventListener' in element)
        element.removeEventListener(realEvent(handler.e), handler.proxy, eventCapture(handler, capture))
      })
    })
  }

  $.event = { add: add, remove: remove }

  $.proxy = function(fn, context) {
    var args = (2 in arguments) && slice.call(arguments, 2)
    if (isFunction(fn)) {
      var proxyFn = function(){ return fn.apply(context, args ? args.concat(slice.call(arguments)) : arguments) }
      proxyFn._zid = zid(fn)
      return proxyFn
    } else if (isString(context)) {
      if (args) {
        args.unshift(fn[context], fn)
        return $.proxy.apply(null, args)
      } else {
        return $.proxy(fn[context], fn)
      }
    } else {
      throw new TypeError("expected function")
    }
  }

  $.fn.bind = function(event, data, callback){
    return this.on(event, data, callback)
  }
  $.fn.unbind = function(event, callback){
    return this.off(event, callback)
  }
  $.fn.one = function(event, selector, data, callback){
    return this.on(event, selector, data, callback, 1)
  }

  var returnTrue = function(){return true},
      returnFalse = function(){return false},
      ignoreProperties = /^([A-Z]|returnValue$|layer[XY]$|webkitMovement[XY]$)/,
      eventMethods = {
        preventDefault: 'isDefaultPrevented',
        stopImmediatePropagation: 'isImmediatePropagationStopped',
        stopPropagation: 'isPropagationStopped'
      }

  function compatible(event, source) {
    if (source || !event.isDefaultPrevented) {
      source || (source = event)

      $.each(eventMethods, function(name, predicate) {
        var sourceMethod = source[name]
        event[name] = function(){
          this[predicate] = returnTrue
          return sourceMethod && sourceMethod.apply(source, arguments)
        }
        event[predicate] = returnFalse
      })

      event.timeStamp || (event.timeStamp = Date.now())

      if (source.defaultPrevented !== undefined ? source.defaultPrevented :
          'returnValue' in source ? source.returnValue === false :
          source.getPreventDefault && source.getPreventDefault())
        event.isDefaultPrevented = returnTrue
    }
    return event
  }

  function createProxy(event) {
    var key, proxy = { originalEvent: event }
    for (key in event)
      if (!ignoreProperties.test(key) && event[key] !== undefined) proxy[key] = event[key]

    return compatible(proxy, event)
  }

  $.fn.delegate = function(selector, event, callback){
    return this.on(event, selector, callback)
  }
  $.fn.undelegate = function(selector, event, callback){
    return this.off(event, selector, callback)
  }

  $.fn.live = function(event, callback){
    $(document.body).delegate(this.selector, event, callback)
    return this
  }
  $.fn.die = function(event, callback){
    $(document.body).undelegate(this.selector, event, callback)
    return this
  }

  $.fn.on = function(event, selector, data, callback, one){
    var autoRemove, delegator, $this = this
    if (event && !isString(event)) { //处理批量绑定事件的情况
      $.each(event, function(type, fn){
        $this.on(type, selector, data, fn, one)
      })
      return $this
    }

    /*
    处理绑定的各种情况，最全的是5个参数，最简单的$el.bind('click', callback)
    */
    if (!isString(selector) && !isFunction(callback) && callback !== false)
      callback = data, data = selector, selector = undefined //这是只有三个参数的情况，1、event-type 2、data 3、callback。类似$el.bind('click', data, callback)
    if (callback === undefined || data === false)
      callback = data, data = undefined //若第三个参数还是未定义，则认为是最简单的情况$el.bind('click', callback)

    if (callback === false) callback = returnFalse //若第二个参数仍未定义，则认为是$el.bind('click')

    return $this.each(function(_, element){
      if (one) autoRemove = function(e){ //若one有效值，这个在第一遍调用后移除监听事件
        remove(element, e.type, callback)
        return callback.apply(this, arguments)
      }

      //若绑定事件使用了选择器，则使用代理函数
      if (selector) delegator = function(e){
        //closest是一个很重要的方法 与parents类似，但只会返回最近的节点
        var evt, match = $(e.target).closest(selector, element).get(0)
        //此处 接收到event后 若检测不匹配 则代理函数为空
        if (match && match !== element) {
          evt = $.extend(createProxy(e), {currentTarget: match, liveFired: element})
          return (autoRemove || callback).apply(match, [evt].concat(slice.call(arguments, 1)))
        }
      }

      add(element, event, callback, data, selector, delegator || autoRemove)
    })
  }
  $.fn.off = function(event, selector, callback){
    var $this = this
    if (event && !isString(event)) {
      $.each(event, function(type, fn){
        $this.off(type, selector, fn)
      })
      return $this
    }

    if (!isString(selector) && !isFunction(callback) && callback !== false)
      callback = selector, selector = undefined

    if (callback === false) callback = returnFalse

    return $this.each(function(){
      remove(this, event, callback, selector)
    })
  }

  //一个相对独立的函数，提供给外部使用
  $.fn.trigger = function(event, args){
    event = (isString(event) || $.isPlainObject(event)) ? $.Event(event) : compatible(event)
    event._args = args
    return this.each(function(){
      // handle focus(), blur() by calling them directly
      if (event.type in focus && typeof this[event.type] == "function") this[event.type]()
      // items in the collection might not be DOM elements
      else if ('dispatchEvent' in this) this.dispatchEvent(event)  //创建一个事件,dispatchEvent一下触发事件，就是这么简单
      else $(this).triggerHandler(event, args)
    })
  }

  // triggers event handlers on current element just as if an event occurred,
  // doesn't trigger an actual event, doesn't bubble
  $.fn.triggerHandler = function(event, args){
    var e, result
    this.each(function(i, element){
      e = createProxy(isString(event) ? $.Event(event) : event)
      e._args = args
      e.target = element
      $.each(findHandlers(element, event.type || event), function(i, handler){
        result = handler.proxy(e)
        if (e.isImmediatePropagationStopped()) return false
      })
    })
    return result
  }

  // shortcut methods for `.bind(event, fn)` for each event type
  ;('focusin focusout focus blur load resize scroll unload click dblclick '+
  'mousedown mouseup mousemove mouseover mouseout mouseenter mouseleave '+
  'change select keydown keypress keyup error').split(' ').forEach(function(event) {
    $.fn[event] = function(callback) {
      return (0 in arguments) ?
        this.bind(event, callback) :
        this.trigger(event) //向外部提供$.click(callback())这种函数调用方式。另外，参数为空就触发对应事件
    }
  })

  //创建事件的基本方法 MouseEvents || Events
  $.Event = function(type, props) {
    if (!isString(type)) props = type, type = props.type
    var event = document.createEvent(specialEvents[type] || 'Events'), bubbles = true
    if (props) for (var name in props) (name == 'bubbles') ? (bubbles = !!props[name]) : (event[name] = props[name])
    event.initEvent(type, bubbles, true)
    return compatible(event)
  }

})(Zepto)