jquery1.7.2的源码分析（五）$.support

$.support 的英文注释很详细的介绍的这里，就稍微的写了下

Query.support = (function() {
var support,
all,
a,
select,
opt,
input,
fragment,
tds,
events,
eventName,
i,
isSupported,
div = document.createElement( "div" ),
documentElement = document.documentElement;
// Preliminary tests
div.setAttribute("className", "t");
div.innerHTML = "


a";
all = div.getElementsByTagName( "*" );
a = div.getElementsByTagName( "a" )[ 0 ];
// Can‘t get basic test support
//不能支持最基本的支持就返回support为空的对象
if ( !all || !all.length || !a ) {
return {};
}
// First batch of supports tests
select = document.createElement( "select" );
opt = select.appendChild( document.createElement("option") );
input = div.getElementsByTagName( "input" )[ 0 ];
support = {
// IE strips leading whitespace when .innerHTML is used IE带空格使用
// 这段代码中，先创建了一个 div ，之后就用 innerHTML 为 div 赋值，
//然后检查 div 的第一个子元素的 nodeType 是否为 3 （表示文本），
       //是的话则空白字符被保留，否则未被保留。
leadingWhitespace: ( div.firstChild.nodeType === 3 ),
//确保tbody没有被自动的插入，在IE中tbody是自动被插入的
// Make sure that tbody elements aren‘t automatically inserted
// IE will insert them into empty tables
tbody: !div.getElementsByTagName("tbody").length,
//确保link被序列化
// Make sure that link elements get serialized correctly by innerHTML
// This requires a wrapper element in IE 在IE中要求一个包含的元素
htmlSerialize: !!div.getElementsByTagName("link").length,
// Get the style information from getAttribute 通过getAttribute得到信息
// (IE uses .cssText instead) IE使用cssText代替
style: /top/.test( a.getAttribute("style") ),
// Make sure that URLs aren‘t manipulated
// (IE normalizes it by default)
hrefNormalized: ( a.getAttribute("href") === "/a" ),
// Make sure that element opacity exists
// (IE uses filter instead)
// Use a regex to work around a WebKit issue. See #5145
opacity: /^0.55/.test( a.style.opacity ),
// Verify style float existence
// (IE uses styleFloat instead of cssFloat)
cssFloat: !!a.style.cssFloat,
// Make sure that if no value is specified for a checkbox
// that it defaults to "on".
// (WebKit defaults to "" instead)
checkOn: ( input.value === "on" ),
// Make sure that a selected-by-default option has a working selected property.
// (WebKit defaults to false instead of true, IE too, if it‘s in an optgroup)
optSelected: opt.selected,
// Test setAttribute on camelCase class. If it works, we need attrFixes when doing get/setAttribute (ie6/7)
getSetAttribute: div.className !== "t",
// Tests for enctype support on a form(#6743)
enctype: !!document.createElement("form").enctype,
// Makes sure cloning an html5 element does not cause problems
// Where outerHTML is undefined, this still works
html5Clone: document.createElement("nav").cloneNode( true ).outerHTML !== "",
// Will be defined later
submitBubbles: true,
changeBubbles: true,
focusinBubbles: false,
deleteExpando: true,
noCloneEvent: true,
inlineBlockNeedsLayout: false,
shrinkWrapBlocks: false,
reliableMarginRight: true,
pixelMargin: true
};
// jQuery.boxModel DEPRECATED in 1.3, use jQuery.support.boxModel instead
jQuery.boxModel = support.boxModel = (document.compatMode === "CSS1Compat");
// Make sure checked status is properly cloned
input.checked = true;
support.noCloneChecked = input.cloneNode( true ).checked;
// Make sure that the options inside disabled selects aren‘t marked as disabled
// (WebKit marks them as disabled)
select.disabled = true;
support.optDisabled = !opt.disabled;
// Test to see if it‘s possible to delete an expando from an element
// Fails in Internet Explorer
try {
delete div.test;
} catch( e ) {
support.deleteExpando = false;
}
if ( !div.addEventListener && div.attachEvent && div.fireEvent ) {
div.attachEvent( "onclick", function() {
// Cloning a node shouldn‘t copy over any
// bound event handlers (IE does this)
support.noCloneEvent = false;
});
div.cloneNode( true ).fireEvent( "onclick" );
}
// Check if a radio maintains its value
// after being appended to the DOM
input = document.createElement("input");
input.value = "t";
input.setAttribute("type", "radio");
support.radioValue = input.value === "t";
input.setAttribute("checked", "checked");
// #11217 - WebKit loses check when the name is after the checked attribute
input.setAttribute( "name", "t" );
div.appendChild( input );
fragment = document.createDocumentFragment();
fragment.appendChild( div.lastChild );
// WebKit doesn‘t clone checked state correctly in fragments
support.checkClone = fragment.cloneNode( true ).cloneNode( true ).lastChild.checked;
// Check if a disconnected checkbox will retain its checked
// value of true after appended to the DOM (IE6/7)
support.appendChecked = input.checked;
fragment.removeChild( input );
fragment.appendChild( div );
// Technique from Juriy Zaytsev
// http://perfectionkills.com/detecting-event-support-without-browser-sniffing/
// We only care about the case where non-standard event systems
// are used, namely in IE. Short-circuiting here helps us to
// avoid an eval call (in setAttribute) which can cause CSP
// to go haywire. See: https://developer.mozilla.org/en/Security/CSP
//这段代码的作用就是检验了IE的冒泡的支持
//$.support[‘changeBubbles‘]
if ( div.attachEvent ) {
for ( i in {
submit: 1,
change: 1,
focusin: 1
}) {
eventName = "on" + i;
isSupported = ( eventName in div );
if ( !isSupported ) {
div.setAttribute( eventName, "return;" );
isSupported = ( typeof div[ eventName ] === "function" );
}
support[ i + "Bubbles" ] = isSupported;
}
}
fragment.removeChild( div );
// Null elements to avoid leaks in IE
fragment = select = opt = div = input = null;
// Run tests that need a body at doc ready
jQuery(function() {
var container, outer, inner, table, td, offsetSupport,
marginDiv, conMarginTop, style, html, positionTopLeftWidthHeight,
paddingMarginBorderVisibility, paddingMarginBorder,
body = document.getElementsByTagName("body")[0];
if ( !body ) {
// Return for frameset docs that don‘t have a body
return;
}
conMarginTop = 1;
paddingMarginBorder = "padding:0;margin:0;border:";
positionTopLeftWidthHeight = "position:absolute;top:0;left:0;width:1px;height:1px;";
paddingMarginBorderVisibility = paddingMarginBorder + "0;visibility:hidden;";
style = "style=‘" + positionTopLeftWidthHeight + paddingMarginBorder + "5px solid #000;";
html = "

" +
"
" +
"


";
container = document.createElement("div");
container.style.cssText = paddingMarginBorderVisibility + "width:0;height:0;position:static;top:0;margin-top:" + conMarginTop + "px";
body.insertBefore( container, body.firstChild );
// Construct the test element
div = document.createElement("div");
container.appendChild( div );
// Check if table cells still have offsetWidth/Height when they are set
// to display:none and there are still other visible table cells in a
// table row; if so, offsetWidth/Height are not reliable for use when
// determining if an element has been hidden directly using
// display:none (it is still safe to use offsets if a parent element is
// hidden; don safety goggles and see bug #4512 for more information).
// (only IE 8 fails this test)
div.innerHTML = "



t



";
tds = div.getElementsByTagName( "td" );
isSupported = ( tds[ 0 ].offsetHeight === 0 );
tds[ 0 ].style.display = "";
tds[ 1 ].style.display = "none";
// Check if empty table cells still have offsetWidth/Height
// (IE 

";
support.shrinkWrapBlocks = ( div.offsetWidth !== 3 );
}
div.style.cssText = positionTopLeftWidthHeight + paddingMarginBorderVisibility;
div.innerHTML = html;
outer = div.firstChild;
inner = outer.firstChild;
td = outer.nextSibling.firstChild.firstChild;
offsetSupport = {
doesNotAddBorder: ( inner.offsetTop !== 5 ),
doesAddBorderForTableAndCells: ( td.offsetTop === 5 )
};
inner.style.position = "fixed";
inner.style.top = "20px";
// safari subtracts parent border width here which is 5px
offsetSupport.fixedPosition = ( inner.offsetTop === 20 || inner.offsetTop === 15 );
inner.style.position = inner.style.top = "";
outer.style.overflow = "hidden";
outer.style.position = "relative";
offsetSupport.subtractsBorderForOverflowNotVisible = ( inner.offsetTop === -5 );
offsetSupport.doesNotIncludeMarginInBodyOffset = ( body.offsetTop !== conMarginTop );
if ( window.getComputedStyle ) {
div.style.marginTop = "1%";
support.pixelMargin = ( window.getComputedStyle( div, null ) || { marginTop: 0 } ).marginTop !== "1%";
}
if ( typeof container.style.zoom !== "undefined" ) {
container.style.zoom = 1;
}
body.removeChild( container );
marginDiv = div = container = null;
jQuery.extend( support, offsetSupport );
});
return support;
})();