jQuery源码学习笔记四

这一节重点讲jQuery对样式的处理，虽然IE同时拥有style,currentStyle与runtimeStyle，但没有一个能获取used value，这是原罪。直接导致的结果是处理样式，就是处理IE的非精确值问题，有时能否获得值也是个大问题。jQuery与其他类库一样，在这方面下了很大工夫，最终在这方面打败其他类库。

//@author  司徒正美|なさみ|cheng http://www.cnblogs.com/rubylouvre/  All rights reserved
      //这里的代码写得很垃圾啊，不过这样写肯定有它的道理，既然版本号已经发展1.32，那当然是那么兼容以前的代码设计的
      className: {
        //顺便一提className与arguments一样是个类数组
        add: function( elem, classNames ) {
          jQuery.each((classNames || "").split(/\s+/), function(i, className){
            if ( elem.nodeType == 1 && !jQuery.className.has( elem.className, className ) )
              elem.className += (elem.className ? " " : "") + className;
          });
        },
 
        // internal only, use removeClass("class")
        remove: function( elem, classNames ) {
          //觉得什么都用自定义函数解决效率太低了，更何况jQuery.grep的逻辑如此复杂
          if (elem.nodeType == 1)
            elem.className = classNames !== undefined ?
            jQuery.grep(elem.className.split(/\s+/), function(className){
            return !jQuery.className.has( classNames, className );
          }).join(" ") :
            "";
        },
 
        // internal only, use hasClass("class")
        has: function( elem, className ) {
          return elem && jQuery.inArray( className, (elem.className || elem).toString().split(/\s+/) ) > -1;
        }
      },
      //这是一个非常重要的内部函数，用于精确获取样式值
      // A method for quickly swapping in/out CSS properties to get correct calculations
      swap: function( elem, options, callback ) {
        var old = {};//备份用
        // Remember the old values, and insert the new ones
        for ( var name in options ) {
          old[ name ] = elem.style[ name ];
          elem.style[ name ] = options[ name ];
        }
        //交换之后调用测试函数
        callback.call( elem );
        //测试完后还原
        // Revert the old values
        for ( var name in options )
          elem.style[ name ] = old[ name ];
      },
      //jQuery对象也有一个与它同名的方法，但这不是简单的代理
      //不过实际路线图为原型的css→原型的attr→静态的attr→静态的css
      //最后是curCSS，这才是真身
      css: function( elem, name, force, extra ) {
        //处理宽与高，因为IE不能正确返回以px为单位的精确值
        if ( name == "width" || name == "height" ) {
          //props用于swap，一个聪明的手段，值得学习
          var val, props = { position: "absolute", visibility: "hidden", display:"block" }, which = name == "width" ? [ "Left", "Right" ] : [ "Top", "Bottom" ];
 
          function getWH() {
            //Ext与Prototypet等类库也是这样实现
            //在标准模式中，offsetWidth是包含padding，borderWidth与width
            //在怪癖模式下，offsetWidth等于width，而width是包含padding与borderWidth
            //offsetHeight同理
            val = name == "width" ? elem.offsetWidth : elem.offsetHeight;
 
            if ( extra === "border" )
              return;
            jQuery.each( which, function() {
              if ( !extra )
              //求出paddingLeft与paddingRight之和，或paddingTop与paddingBottom之和，
              //然后作为减数，去减offsetWidth或offsetHeight
                val -= parseFloat(jQuery.curCSS( elem, "padding" + this, true)) || 0;
              if ( extra === "margin" )
 
              val += parseFloat(jQuery.curCSS( elem, "margin" + this, true)) || 0;
            else
              val -= parseFloat(jQuery.curCSS( elem, "border" + this + "Width", true)) || 0;
          });
        }
        if ( elem.offsetWidth !== 0 )
          getWH();
        else
        //如果display:none就求不出offsetWidht与offsetHeight，swap一下
          jQuery.swap( elem, props, getWH );
        return Math.max(0, Math.round(val));
      }
      //再调用jQuery.curCSS进行深加工
      return jQuery.curCSS( elem, name, force );
    },
 
    curCSS: function( elem, name, force ) {
      var ret, style = elem.style;
 
      // We need to handle opacity special in IE
      if ( name == "opacity" && !jQuery.support.opacity ) {
        ret = jQuery.attr( style, "opacity" );
 
        return ret == "" ?
          "1" :
          ret;
      }
 
      // Make sure we're using the right name for getting the float value
      if ( name.match( /float/i ) )
        name = styleFloat;
 
      if ( !force && style && style[ name ] )
        ret = style[ name ];//缓存结果
 
      else if ( defaultView.getComputedStyle ) {
        //标准浏览器
        // Only "float" is needed here
        if ( name.match( /float/i ) )
          name = "float";//把cssFloat转换为float
        //把驼峰风格转换为连字符风格
        name = name.replace( /([A-Z])/g, "-$1" ).toLowerCase();
 
        var computedStyle = defaultView.getComputedStyle( elem, null );
        if ( computedStyle )
          ret = computedStyle.getPropertyValue( name );
 
        // We should always get a number back from opacity
        if ( name == "opacity" && ret == "" )
          ret = "1";//把opacity设置成1
 
      } else if ( elem.currentStyle ) {
        //IE浏览器部分
        var camelCase = name.replace(/\-(\w)/g, function(all, letter){
          return letter.toUpperCase();
        });
        //把连字符风格转换为驼峰风格
        ret = elem.currentStyle[ name ] || elem.currentStyle[ camelCase ];
        // From the awesome hack by Dean Edwards
        // http://erik.eae.net/archives/2007/07/27/18.54.15/#comment-102291
 
        // If we're not dealing with a regular pixel number
        // but a number that has a weird ending, we need to convert it to pixels
        //将不是以px为单位的计算值全部转换为以px为单位，用到 Dean Edwards（Base2类库的作者）的hack
        //网上有文章讲解这hach，这里不重复
        if ( !/^\d+(px)?$/i.test( ret ) && /^\d/.test( ret ) ) {
          // Remember the original values
          var left = style.left, rsLeft = elem.runtimeStyle.left;
          // Put in the new values to get a computed value out
          elem.runtimeStyle.left = elem.currentStyle.left;
          style.left = ret || 0;
          ret = style.pixelLeft + "px";
          // Revert the changed values
          style.left = left;
          elem.runtimeStyle.left = rsLeft;
        }
      }
      return ret;
    },
    attr: function( elem, name, value ) {
      // 文本，注释节点不处理
      if (!elem || elem.nodeType == 3 || elem.nodeType == 8)
        return undefined;
      //不处理xml文档的
      var notxml = !jQuery.isXMLDoc( elem ),
      //是读方法还是写方法
      set = value !== undefined;
 
      // Try to normalize/fix the name
      //兼容处理，
      //jQuery.props = {
      //"for": "htmlFor",
      //"class": "className",
      //"float": styleFloat,
      //cssFloat: styleFloat,
      //styleFloat: styleFloat,
      //readonly: "readOnly",
      //maxlength: "maxLength",
      //cellspacing: "cellSpacing",
      //rowspan: "rowSpan",
      //tabindex: "tabIndex"
      //};
      name = notxml && jQuery.props[ name ] || name;
 
      // Only do all the following if this is a node (faster for style)
      // IE elem.getAttribute passes even for style
      if ( elem.tagName ) {
 
        // These attributes require special treatment
        var special = /href|src|style/.test( name );
 
        // Safari mis-reports the default selected property of a hidden option
        // Accessing the parent's selectedIndex property fixes it
        //修正无法取得selected正确值的bug
        if ( name == "selected" && elem.parentNode )
          elem.parentNode.selectedIndex;
 
        // If applicable, access the attribute via the DOM 0 way
        if ( name in elem && notxml && !special ) {
          if ( set ){
            //不允许改写type的值
            // We can't allow the type property to be changed (since it causes problems in IE)
            if ( name == "type" && jQuery.nodeName( elem, "input" ) && elem.parentNode )
              throw "type property can't be changed";
 
            elem[ name ] = value;
          }
 
          // browsers index elements by id/name on forms, give priority to attributes.
          if( jQuery.nodeName( elem, "form" ) && elem.getAttributeNode(name) )
          //getAttributeNode() 方法的作用是：通过指定的名称获取当前元素中的属性节点。
            return elem.getAttributeNode( name ).nodeValue;
 
          // elem.tabIndex doesn't always return the correct value when it hasn't been explicitly set
          // http://fluidproject.org/blog/2008/01/09/getting-setting-and-removing-tabindex-values-with-javascript/
          //IE只能tabIndex
          //标准浏览器用tabindex
          if ( name == "tabIndex" ) {
            var attributeNode = elem.getAttributeNode( "tabIndex" );
            return attributeNode && attributeNode.specified
              ? attributeNode.value
            : elem.nodeName.match(/(button|input|object|select|textarea)/i)
              ? 0
            : elem.nodeName.match(/^(a|area)$/i) && elem.href
              ? 0
            : undefined;
          }
 
          return elem[ name ];
        }
 
        if ( !jQuery.support.style && notxml &&  name == "style" )
          return jQuery.attr( elem.style, "cssText", value );
 
        if ( set )
        // convert the value to a string (all browsers do this but IE) see #1070
          elem.setAttribute( name, "" + value );
        //IE的getAttribute支持第二个参数，可以为 0,1,2
        //0 是默认；1 区分属性的大小写；2取出源代码中的原字符串值。
        //IE 在取 href 的时候默认拿出来的是绝对路径，加参数2得到我们所需要的相对路径。
        var attr = !jQuery.support.hrefNormalized && notxml && special
        // Some attributes require a special call on IE
          ? elem.getAttribute( name, 2 )
        : elem.getAttribute( name );
 
        // Non-existent attributes return null, we normalize to undefined
        return attr === null ? undefined : attr;
      }
 
      // elem is actually elem.style ... set the style
 
      // IE uses filters for opacity
      if ( !jQuery.support.opacity && name == "opacity" ) {
        if ( set ) {
          // IE has trouble with opacity if it does not have layout
          // Force it by setting the zoom level
          //IE7中滤镜（filter）必须获得hasLayout才能生效，我们用zoom这个IE私有属性让其获得hasLayout
          elem.zoom = 1;
 
          // Set the alpha filter to set the opacity
          elem.filter = (elem.filter || "").replace( /alpha\([^)]*\)/, "" ) +
            (parseInt( value ) + '' == "NaN" ? "" : "alpha(opacity=" + value * 100 + ")");
        }
 
        return elem.filter && elem.filter.indexOf("opacity=") >= 0 ?
          (parseFloat( elem.filter.match(/opacity=([^)]*)/)[1] ) / 100) + '':
          "";
      }
      //获得其他属性，直接用DOM 0方法读写
      name = name.replace(/-([a-z])/ig, function(all, letter){
        return letter.toUpperCase();
      });
 
      if ( set )
        elem[ name ] = value;
 
      return elem[ name ];
    },

其实在curCss与attr方法中还夹着一个clean方法，总觉得clean职责太多，里面分支繁缛，看得我头晕眼花……太凌乱，这方法应该分割成几个方法条理更清晰，效率更高。

//把字符串转换为DOM元素的纯数组
//这里的elems为字符串数组，将用文档碎片做转换
clean: function( elems, context, fragment ) {
  context = context || document;
 
  // !context.createElement fails in IE with an error but returns typeof 'object'
  if ( typeof context.createElement === "undefined" )
    context = context.ownerDocument || context[0] && context[0].ownerDocument || document;
 
  // If a single string is passed in and it's a single tag
  // just do a createElement and skip the rest
 
  if ( !fragment && elems.length === 1 && typeof elems[0] === "string" ) {
    var match = /^<(\w+)\s*\/?>$/.exec(elems[0]);
    if ( match )
      return [ context.createElement( match[1] ) ];
  }
  //div是用于把字符串转换为DOM的
  var ret = [], scripts = [], div = context.createElement("div");
  jQuery.each(elems, function(i, elem){
    if ( typeof elem === "number" )
      elem += '';//转换为字符串
 
    if ( !elem )
      return;
 
    // Convert html string into DOM nodes
    if ( typeof elem === "string" ) {
      // Fix "XHTML"-style tags in all browsers
      //生成闭合的标签对，亦即把在XHTML中不合法的写法强制转换过来
      elem = elem.replace(/(<(\w+)[^>]*?)\/>/g, function(all, front, tag){
        //但对于abbr|br|col|img|input|link|meta|param|hr|area|embed等元素不修改
        return tag.match(/^(abbr|br|col|img|input|link|meta|param|hr|area|embed)$/i) ?
          all :
          front + "></" + tag + ">";
      });
 
      // Trim whitespace, otherwise indexOf won't work as expected
      //将“ <div> ”去掉两边的空白“<div>”，用于下面的indexOf
      var tags = elem.replace(/^\s+/, "").substring(0, 10).toLowerCase();
 
      var wrap =
        // option or optgroup
      //option与optgroup的直接父元素一定是select
        !tags.indexOf("<opt") &&
        [ 1, "<select multiple='multiple'>", "</select>" ] ||
        //legend的直接父元素一定是fieldset
        !tags.indexOf("<leg") &&
        [ 1, "<fieldset>", "</fieldset>" ] ||
        //thead,tbody,tfoot,colgroup,caption的直接父元素一定是table
      tags.match(/^<(thead|tbody|tfoot|colg|cap)/) &&
        [ 1, "<table>", "</table>" ] ||
        //tr的直接父元素一定是tbody，
        !tags.indexOf("<tr") &&
        [ 2, "<table><tbody>", "</tbody></table>" ] ||
        //<thead> matched above
      //td与th的直接父元素一定是tr
      (!tags.indexOf("<td") || !tags.indexOf("<th")) &&
        [ 3, "<table><tbody><tr>", "</tr></tbody></table>" ] ||
        //col一定是colgroup
        !tags.indexOf("<col") &&
        [ 2, "<table><tbody></tbody><colgroup>", "</colgroup></table>" ] ||
 
        // IE can't serialize <link> and <script> tags normally
        !jQuery.support.htmlSerialize &&
        [ 1, "div<div>", "</div>" ] ||
 
        [ 0, "", "" ];
 
      // Go to html and back, then peel off extra wrappers
      div.innerHTML = wrap[1] + elem + wrap[2];
 
      // Move to the right depth
      while ( wrap[0]-- )
        div = div.lastChild;
      //IE会自动添加tbody，要特殊处理
      // Remove IE's autoinserted <tbody> from table fragments
      if ( !jQuery.support.tbody ) {
 
        // String was a <table>, *may* have spurious <tbody>
        var hasBody = /<tbody/i.test(elem),
        tbody = !tags.indexOf("<table") && !hasBody ?
          div.firstChild && div.firstChild.childNodes :
 
          // String was a bare <thead> or <tfoot>
        wrap[1] == "<table>" && !hasBody ?
          div.childNodes :
          [];
 
        for ( var j = tbody.length - 1; j >= 0 ; --j )
          if ( jQuery.nodeName( tbody[ j ], "tbody" ) && !tbody[ j ].childNodes.length )
            tbody[ j ].parentNode.removeChild( tbody[ j ] );
 
      }
 
      // IE completely kills leading whitespace when innerHTML is used
      if ( !jQuery.support.leadingWhitespace && /^\s/.test( elem ) )
        div.insertBefore( context.createTextNode( elem.match(/^\s*/)[0] ), div.firstChild );
      //div中的所有节点都转换为数组
      elem = jQuery.makeArray( div.childNodes );
    }
 
    if ( elem.nodeType )
    //过滤非元素节点的节点
      ret.push( elem );
    else
    //把符合要求的节点加入ret中
      ret = jQuery.merge( ret, elem );
 
  });
 
  if ( fragment ) {
    for ( var i = 0; ret[i]; i++ ) {
      //处理script元素
      if ( jQuery.nodeName( ret[i], "script" ) && (!ret[i].type || ret[i].type.toLowerCase() === "text/javascript") ) {
        scripts.push( ret[i].parentNode ? ret[i].parentNode.removeChild( ret[i] ) : ret[i] );
      } else {
        if ( ret[i].nodeType === 1 )
          ret.splice.apply( ret, [i + 1, 0].concat(jQuery.makeArray(ret[i].getElementsByTagName("script"))) );
        fragment.appendChild( ret[i] );
      }
    }
 
    return scripts;
  }
 
  return ret;
},