jQuery.support
jQuery.support 用于检查浏览器对各项特性的支持。检查项多达 27 个。
首先，让我们用一段代码测试一下 support 中包含的检查项：
<、script src="jquery.js"><、script>
support = $.support;
for (key in support) {
document.write('support.' + key + ' = ' + support[key] + '换行符');
}
IE 下的输出结果为：
support.leadingWhitespace = false
support.tbody = false
support.htmlSerialize = false
support.style = false
support.hrefNormalized = false
support.opacity = false
support.cssFloat = false
support.checkOn = true
support.optSelected = false
support.getSetAttribute = false
support.submitBubbles = false
support.changeBubbles = false
support.focusinBubbles = true
support.deleteExpando = false
support.noCloneEvent = false
support.inlineBlockNeedsLayout = false
support.shrinkWrapBlocks = true
support.reliableMarginRight = true
support.noCloneChecked = false
support.optDisabled = true
support.radioValue = false
support.checkClone = undefined
support.appendChecked = false
support.boxModel = false
support.reliableHiddenOffsets = false
support.ajax = true
support.cors = false
FireFox 中的显示结果为：
support.leadingWhitespace = true
support.tbody = true
support.htmlSerialize = true
support.style = true
support.hrefNormalized = true
support.opacity = true
support.cssFloat = true
support.checkOn = true
support.optSelected = true
support.getSetAttribute = true
support.submitBubbles = true
support.changeBubbles = true
support.focusinBubbles = false
support.deleteExpando = true
support.noCloneEvent = true
support.inlineBlockNeedsLayout = false
support.shrinkWrapBlocks = false
support.reliableMarginRight = true
support.noCloneChecked = true
support.optDisabled = true
support.radioValue = true
support.checkClone = undefined
support.appendChecked = true
support.boxModel = true
support.reliableHiddenOffsets = true
support.ajax = true
support.cors = true
需要注意的是，源代码中 checkClone 的检查是有问题的。这将在后面提到。 接下来，我们就对这些检查项进行逐一的分析。
leadingWhitespace
检查用 innerHTML 赋值时，是否会保留前面的空白符。
IE中为 false ， Firefox 中为 true 。
实现方式如下：
$ = function(){
// Other codes ...
var support = {
leadingWhitespace: (div.firstChild.nodeType === 3),
tbody: !div.getElementsByTagName("tbody").length
}
// Other codes ...
}();
这段代码在原有基础上为 support 增加了 tbody 属性， 并检查是否能够获取 tbody 标签。由于 innerHTML 中已经包含了 table 标签，能获取 tbody 标签的话则表示会自动为 table 插入 tbody，否则表示不会自动插入 tbody 。