jQuery源碼解析之click()的事件綁定

前言:
這篇依舊長,請耐心看下去。html

1、事件委託
DOM有個事件流特性,因此觸發DOM節點的時候,會經歷3個階段:
(1)階段一:Capturing 事件捕獲(從祖到目標)
事件自上(document->html->body->xxx)而下到達目標節點的過程當中,瀏覽器會檢測 針對該事件的 監聽器(用來捕獲事件),並運行捕獲事件的監聽器node

(2)階段二:Target 目標
瀏覽器找到監聽器後,就運行該監聽器api

(3)階段三:Bubbling 冒泡(目標到祖)
事件自下而上(document->html->body->xxx)到達目標節點的過程當中,瀏覽器會檢測不是 針對該事件的 監聽器(用來捕獲事件),並運行非捕獲事件的監聽器數組

2、$().click()
做用:
爲目標元素綁定點擊事件瀏覽器

源碼:app

//這種寫法還第一次見,將全部鼠標事件寫成字符串再換成數組
  //再一一綁定到DOM節點上去
  //源碼10969行
  jQuery.each( ( "blur focus focusin focusout resize scroll click dblclick " +
    "mousedown mouseup mousemove mouseover mouseout mouseenter mouseleave " +
    "change select submit keydown keypress keyup contextmenu" ).split( " " ),
    function( i, name ) {
      //事件綁定
      // Handle event binding
      jQuery.fn[ name ] = function( data, fn ) {
        return arguments.length > 0 ?
          //若是有參數的話,就用jQuery的on綁定
          this.on( name, null, data, fn ) :
          //不然使用trigger
          this.trigger( name );
      };
    } );

解析:
能夠看到,jQuery 將全部的鼠標事件都一一列舉了出來,並經過jQuery.fn[ name ] = function( data, fn ) { xxx }dom

若是有參數,則是綁定事件,調用 on() 方法;
沒有參數,則是調用事件,調用 trigger() 方法( trigger() 放到下篇講 )ide

3、$().on()
做用:
在被選元素及子元素上添加一個或多個事件處理程序函數

源碼:ui

//綁定事件的方法
  //源碼5812行
  jQuery.fn.extend( {
    //在被選元素及子元素上添加一個或多個事件處理程序
    //$().on('click',function()=<{})
    //源碼5817行
    on: function( types, selector, data, fn ) {
      return on( this, types, selector, data, fn );
    },
    //xxx
    //xxx
})

最終調用的是 jQuery.on() 方法:

//綁定事件的on方法
  //源碼5143行
  //目標元素,類型(click,mouseenter,focusin,xxx),回調函數function(){xxx}
  function on( elem, types, selector, data, fn, one ) {
    var origFn, type;
    //這邊能夠不看
    // Types can be a map of types/handlers
    if ( typeof types === "object" ) {

      // ( types-Object, selector, data )
      if ( typeof selector !== "string" ) {

        // ( types-Object, data )
        data = data || selector;
        selector = undefined;
      }
      for ( type in types ) {
        on( elem, type, selector, data, types[ type ], one );
      }
      return elem;
    }
    //直接調用$().on()的話會走這邊
    if ( data == null && fn == null ) {

      // ( types, fn )
      //fn賦值爲selector,即function(){}
      fn = selector;
      //再將selector置爲undefined
      //注意這個寫法,連等賦值
      data = selector = undefined;
    }
    //調用像$().click()的話會走這邊
    else if ( fn == null ) {
      if ( typeof selector === "string" ) {

        // ( types, selector, fn )
        fn = data;
        data = undefined;
      } else {
        
        // ( types, data, fn )
        fn = data;
        data = selector;
        selector = undefined;
      }
    }

    if ( fn === false ) {

      fn = returnFalse;

    } else if ( !fn ) {

      return elem;

    }
    //one()走這裏
    if ( one === 1 ) {
      //將fn賦給origFn後,再定義fn
      origFn = fn;
      fn = function( event ) {
        //將綁定給目標元素的事件傳給fn,
        //並經過$().off()卸載掉
        // Can use an empty set, since event contains the info
        jQuery().off( event );
        //在origFn運行一次的基礎上,讓origFn調用fn方法,arguments即event
        return origFn.apply( this, arguments );
      };
      //讓fn和origFn使用相同的guid,這樣就能移除origFn方法
      // Use same guid so caller can remove using origFn
      fn.guid = origFn.guid || ( origFn.guid = jQuery.guid++ );
    }

    return elem.each( function() {
      //最終調動$.event.add方法
      jQuery.event.add( this, types, fn, data, selector );

    } );
  }

解析:
能夠看到,因爲將 bind()、live() 和 delegate() 都合併進 on() 後,on() 裏面的狀況挺複雜的, data、selector、fn 相互賦值。

注意下 if ( one === 1 ) 這種狀況,是 $().one()on()裏的具體實現,即調用一次on()後,就執行jQuery().off( event ),卸載事件。

該方法最終調用 jQuery.event.add( ) 方法

4、jQuery.event.add( )
做用:
爲目標元素添加事件

源碼:

//源碼5235行
  /*
 * Helper functions for managing events -- not part of the public interface.
 * Props to Dean Edwards' addEvent library for many of the ideas.
 */
  jQuery.event = {

    global: {},
    //源碼5241行
    //this, types, fn, data, selector
    add: function( elem, types, handler, data, selector ) {

      var handleObjIn, eventHandle, tmp,
        events, t, handleObj,
        special, handlers, type, namespaces, origType,
        //elemData正是目標元素jQuery中的id屬性
        //初始值是{}
        elemData = dataPriv.get( elem );
      // Don't attach events to noData or text/comment nodes (but allow plain objects)
      if ( !elemData ) {
        return;
      }
      //調用者能夠傳入一個自定義數據對象來代替處理程序
      // Caller can pass in an object of custom data in lieu of the handler
      if ( handler.handler ) {
        handleObjIn = handler;
        handler = handleObjIn.handler;
        selector = handleObjIn.selector;
      }
      //確保不正確的選擇器會拋出異常
      // Ensure that invalid selectors throw exceptions at attach time
      // Evaluate against documentElement in case elem is a non-element node (e.g., document)
      if ( selector ) {
        jQuery.find.matchesSelector( documentElement, selector );
      }

      //確保handler有惟一的id
      // Make sure that the handler has a unique ID, used to find/remove it later
      if ( !handler.guid ) {
        handler.guid = jQuery.guid++;
      }
      //若是事件處理沒有,則置爲空對象
      // Init the element's event structure and main handler, if this is the first
      //在這裏,就應經給events賦值了,
      // 注意這種寫法:賦值的同時,判斷
      if ( !( events = elemData.events ) ) {
        events = elemData.events = {};
      }

      if ( !( eventHandle = elemData.handle ) ) {
        eventHandle = elemData.handle = function( e ) {

          //當在一個頁面卸載後調用事件時,取消jQuery.event.trigger()的第二個事件
          // Discard the second event of a jQuery.event.trigger() and
          // when an event is called after a page has unloaded

          //jQuery.event.triggered: undefined
          //e.type: click/mouseout
          return typeof jQuery !== "undefined" && jQuery.event.triggered !== e.type ?
            //讓elem調用jQuery.event.dispatch方法,參數是arguments
            jQuery.event.dispatch.apply( elem, arguments ) : undefined;
        };
      }
      //經過空格將多個events分開,通常爲一個,如click
      // Handle multiple events separated by a space
      types = ( types || "" ).match( rnothtmlwhite ) || [ "" ];
      t = types.length;
      while ( t-- ) {
        tmp = rtypenamespace.exec( types[ t ] ) || [];
        //click
        type = origType = tmp[ 1 ];
        //""
        namespaces = ( tmp[ 2 ] || "" ).split( "." ).sort();
        // There *must* be a type, no attaching namespace-only handlers
        if ( !type ) {
          continue;
        }
        //若是event改變了它本身的type,就使用特殊的event handlers
        // If event changes its type, use the special event handlers for the changed type
        special = jQuery.event.special[ type ] || {};
        //若是選擇器已定義,肯定一個特殊event api的type
        //不然使用默認type
        // If selector defined, determine special event api type, otherwise given type
        type = ( selector ? special.delegateType : special.bindType ) || type;
        //不明白爲何在上面要先寫一遍
        // Update special based on newly reset type
        special = jQuery.event.special[ type ] || {};
        //handleObj會傳遞給全部的event handlers
        // handleObj is passed to all event handlers
        handleObj = jQuery.extend( {
          type: type,
          origType: origType,
          data: data,
          handler: handler,
          guid: handler.guid,
          selector: selector,
          needsContext: selector && jQuery.expr.match.needsContext.test( selector ),
          namespace: namespaces.join( "." )
        }, handleObjIn );
        
        //第一次綁定事件,走這裏
        // Init the event handler queue if we're the first
        if ( !( handlers = events[ type ] ) ) {
          handlers = events[ type ] = [];
          handlers.delegateCount = 0;

          // Only use addEventListener if the special events handler returns false
          if ( !special.setup ||
            special.setup.call( elem, data, namespaces, eventHandle ) === false ) {
            //目標元素有addEventListener的話,調用綁定click事件
            if ( elem.addEventListener ) {
              elem.addEventListener( type, eventHandle );
            }
          }
        }
        //special的add/handleObj.handler.guidd的初始化處理
        if ( special.add ) {
          special.add.call( elem, handleObj );

          if ( !handleObj.handler.guid ) {
            handleObj.handler.guid = handler.guid;
          }
        }

        // Add to the element's handler list, delegates in front
        if ( selector ) {
          handlers.splice( handlers.delegateCount++, 0, handleObj );
        } else {
          handlers.push( handleObj );
        }
        //一旦有綁定事件,全局通知
        // Keep track of which events have ever been used, for event optimization
        jQuery.event.global[ type ] = true;
      }

    },

...
...

}

解析:
能夠看到,不少的 if 判斷,都是在初始化對象,最後經過 while 循環,調用目標元素的 addEventListener 事件,也就是說,click()/on() 的本質是 element.addEventListener() 事件,前面一系列的鋪墊,都是在爲目標 jQuery 對象添加必要的屬性。

注意寫法 if ( !( events = elemData.events ) ),在賦值的同時,判斷條件

(1)dataPriv

//取惟一id
  //源碼4361行
  var dataPriv = new Data();

在 jQuery 對象中,有惟一id的屬性

$("#one")

elemData = dataPriv.get( elem )

① Data()

//目標元素的jQuery id
  //源碼4209行
  function Data() {
    this.expando = jQuery.expando + Data.uid++;
  }

② jQuery.expando

jQuery.extend( {
    //至關於jQuery爲每個元素取惟一的id
    ///\D/g : 去掉非數字的字符
    // Unique for each copy of jQuery on the page
    //源碼360行
    expando: "jQuery" + ( version + Math.random() ).replace( /\D/g, "" ),
    ...  
    ...
})

③ Math.random()
僞隨機,到小數點後16位

expando: "jQuery" + ( version + Math.random() ).replace( /\D/g, "" ),

能夠看到 jQuery 的 id 是由 jQuery + 版本號+ Math.random() 生成的

關於 Math.random() 是如何生成僞隨機數的請看:https://www.zhihu.com/question/22818104

(2)rtypenamespace

var
    rkeyEvent = /^key/,
    rmouseEvent = /^(?:mouse|pointer|contextmenu|drag|drop)|click/,
    //事件類型的命名空間
    //舉例:var arr1 = "click.aaa.bbb".match(rtypenamespace);
    //console.log(arr1);//["click.aaa.bbb", "click", "aaa.bbb", index: 0, input: "click.aaa.bbb"]
    //源碼5131行
    rtypenamespace = /^([^.]*)(?:\.(.+)|)/;

綜上,綁定事件的本質即調用element.addEventListener()方法,但 jQuery 有太多的狀況須要考慮了。


(完)

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