相关知识：
window.getComputedStyle:
Window.getComputedStyle() 方法给出应用活动样式表后的元素的所有css属性的值，并解析这些值可能包含的任何基本计算。
语法：let style = window.getComputedStyle(element, [pseudoElt]);
pseudoElt ：指定一个要匹配的伪元素的字符串。必须对普通元素省略（或null）。
返回的样式是一个实时的 CSSStyleDeclaration 对象，当元素的样式更改时，它会自动更新本身。
与伪元素一起使用：
let h3 = document.querySelector('h3'),
result = getComputedStyle(h3, '::after').content;
getComputedStyle(odiv,false)这里的两个参数，第一个参数代表要获取那个元素的样式， 第二个是解决FF较低版本的写法，而对于高版本的可以不用写。
注：在firefox3.6上访问子框架内的样式 (iframe)必须使用 document.defaultView.getComputedStyle ,其他可使用window.getComputedStyle
Element.currentStyle
表示由全局样式表，内联样式和HTML属性指定的对象的级联格式和样式。Element.currentStyle 是一个与 window.getComputedStyle方法功能相同的属性。
这个属性实现在旧版本的IE浏览器中.
常用方法：getAttribute、getPropertyValue、setAttribute、setProperty...
常用属性：background、backgroundColor、border、borderBottom...
Element.runtimeStyle
Element.runtimeStyle 是一个自带的属性，和 HTMLElement.style 相似。相比而言, runtimeStyle 具有更高的优先级，但它并不会修改 style 的 content 属性。runtimeStyle 在旧版的IE浏览器上是可用的。
html：
<body> <div style="background:red;" id ="div1"></div> <div style="background:green;" id ="div2"></div> </body>
js：
//获取行间样式 var oDiv=document.getElementById("div1"); console.log(oDiv.style.background);
/*获取非行间样式*/ function getStyle1(obj,attr){ if(obj.currentStyle){//IE return obj.currentStyle[attr]; }else{ //return window.getComputedStyle(obj,false)[attr]; // 或 return document.defaultView.getComputedStyle(obj,null).getPropertyValue(attr); return document.defaultView.getComputedStyle(obj,false)[attr]; } } var oDiv2 =document.getElementById("div2"); console.log(getStyle1(oDiv2,"background"));
/*兼容1*/ /*https://stackoverflow.com/questions/9183555/whats-the-point-of-document-defaultview*/ function getStyle2(element, styleProp) { var view = element.ownerDocument && element.ownerDocument.defaultView ? element.ownerDocument.defaultView : window; return view.getComputedStyle ? view.getComputedStyle(element,null).getPropertyValue(styleProp) : element.currentStyle ? element.currentStyle[styleProp] : null; }
jquery中兼容处理(jQuery JavaScript Library v1.12.4)
/*jquery中兼容处理*/ var ralpha = /alpha([^)]*)/i, ropacity = /opacitys*=s*([^)]*)/i, // swappable if display is none or starts with table except // "table", "table-cell", or "table-caption" // see here for display values: // https://developer.mozilla.org/en-US/docs/CSS/display rdisplayswap = /^(none|table(?!-c[ea]).+)/, rnumsplit = new RegExp( "^(" + pnum + ")(.*)$", "i" ), cssShow = { position: "absolute", visibility: "hidden", display: "block" }, cssNormalTransform = { letterSpacing: "0", fontWeight: "400" }, cssPrefixes = [ "Webkit", "O", "Moz", "ms" ], emptyStyle = document.createElement( "div" ).style; var rnumnonpx = new RegExp( "^(" + pnum + ")(?!px)[a-z%]+$", "i" ); var getStyle,curCSS, rposition = /^(top|right|bottom|left)$/; if(window.getComputedStyle){ // Support: IE<=11+, Firefox<=30+ (#15098, #14150) // IE throws on elements created in popups IE在弹窗中创建元素时抛出错误 // FF meanwhile throws on frame elements through "defaultView.getComputedStyle" // 同时FF在框架frame中使用"defaultView.getComputedStyle"会抛出错误 getStyle = function(elem){ //Node.ownerDocument 只读属性会返回当前节点的顶层的 document 对象。 //注意：被此属性返回的 document 对象是在实际的HTML文档中的所有子节点所属的主对象。 // 如果在文档节点自身上使用此属性，则结果是null。 //var win = document.defaultView; // 在浏览器中，该属性返回当前 document 对象所关联的 window 对象，如果没有（ie8？），会返回 null。 // jquery(#15098, #14150) 它曾经使用window.getComputedStyle，无论哪个文档拥有该节点，并且现在使用（看似更正确的） // ownerDocument.defaultView访问相关窗口（例如，在iframe或弹出窗口中）并在其中调用getComputedStyle。 var view = elem.ownerDocument.defaultView; // opener 属性是一个可读可写的属性，可返回对创建该窗口的 Window 对象的引用。 //opener 属性非常有用，创建的窗口可以引用创建它的窗口所定义的属性和函数。 //注释：只有表示顶层窗口的 Window 对象的 operner 属性才有效，表示框架的 Window 对象的 operner 属性无效。 // opener代表打开自身的那个窗口，比如窗口a.html打开窗口b.html。 // 如果靠window.open方法，则对于窗口b.html，self代表b.html自己，而opener代表窗口a.html。 // myWindow=window.open('','MyName','width=200,height=100') // myWindow.document.write("This is 'myWindow'") // myWindow.focus() // myWindow.opener.document.write("This is the parent window") if(!view||!view.opener){//如果是框架则使用window view = window; } } curCSS = function( elem, name, computed ) { var width, minWidth, maxWidth, ret, style = elem.style; computed = computed || getStyles( elem ); // getPropertyValue is only needed for .css('filter') in IE9, see #12537 //getPropertyValue仅在IE9中.css（'filter'）需要，请参见＃12537;element.css('filter') returns undefined in IE9 ret = computed ? computed.getPropertyValue( name ) || computed[ name ] : undefined; // Support: Opera 12.1x only // Fall back to style even without computed // computed is undefined for elems on document fragments 对文档片段上的elems计算undefined if ( ( ret === "" || ret === undefined ) && !jQuery.contains( elem.ownerDocument, elem ) ) { ret = jQuery.style( elem, name ); } if ( computed ) { // A tribute to the "awesome hack by Dean Edwards" // Chrome < 17 and Safari 5.0 uses "computed value" // instead of "used value" for margin-right // Safari 5.1.7 (at least) returns percentage for a larger set of values, // but width seems to be reliably pixels // this is against the CSSOM draft spec: // http://dev.w3.org/csswg/cssom/#resolved-values // Chrome < 17 and Safari 5.0 的margin-right使用“计算值”而不是“应用值” //Safari 5.1.7 (at least)返回一组百分比，但宽度似乎是可靠的像素,这是有背CSSOM草案规范 if ( !support.pixelMarginRight() && rnumnonpx.test( ret ) && rmargin.test( name ) ) { // Remember the original values width = style.width; minWidth = style.minWidth; maxWidth = style.maxWidth; // Put in the new values to get a computed value out style.minWidth = style.maxWidth = style.width = ret; ret = computed.width; // Revert the changed values style.width = width; style.minWidth = minWidth; style.maxWidth = maxWidth; } } // Support: IE // IE returns zIndex value as an integer. return ret === undefined ? ret : ret + ""; }; }else if(documentElement.currentStyle){ getStyle = function(elem){ return elem.currentStyle; } curCSS = function( elem, name, computed ) { var left, rs, rsLeft, ret, style = elem.style; computed = computed || getStyles( elem ); ret = computed ? computed[ name ] : undefined; // Avoid setting ret to empty string here // so we don't default to auto // 避免将ret设置为空字符串，因此我们不会默认为auto if ( ret == null && style && style[ name ] ) { ret = style[ name ]; } // 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 // but not position css attributes, as those are // proportional to the parent element instead // and we can't measure the parent instead because it // might trigger a "stacking dolls" problem //如果我们不处理正常的像素数 // 但一个数字有一个奇怪的结尾，我们需要将其转换为像素 //但不是位置css属性，因为它们与父元素成比例，我们不能测量父级元素， // 因为它可能会触发“堆叠”问题 if ( rnumnonpx.test( ret ) && !rposition.test( name ) ) { // Remember the original values left = style.left; rs = elem.runtimeStyle; rsLeft = rs && rs.left; // Put in the new values to get a computed value out if ( rsLeft ) { rs.left = elem.currentStyle.left; } style.left = name === "fontSize" ? "1em" : ret; ret = style.pixelLeft + "px"; // Revert the changed values style.left = left; if ( rsLeft ) { rs.left = rsLeft; } } // Support: IE // IE returns zIndex value as an integer. return ret === undefined ? ret : ret + "" || "auto"; }; jQuery.extend( { // Add in style property hooks for overriding the default // behavior of getting and setting a style property //添加样式属性钩子，以覆盖获取和设置样式属性的默认行为 cssHooks: { opacity: { get: function( elem, computed ) { if ( computed ) { // We should always get a number back from opacity var ret = curCSS( elem, "opacity" ); return ret === "" ? "1" : ret; } } } }, // Don't automatically add "px" to these possibly-unitless properties //不要自动添加“px”到这些可能无单位的属性 cssNumber: { "animationIterationCount": true, "columnCount": true, "fillOpacity": true, "flexGrow": true, "flexShrink": true, "fontWeight": true, "lineHeight": true, "opacity": true, "order": true, "orphans": true, "widows": true, "zIndex": true, "zoom": true }, // Add in properties whose names you wish to fix before // setting or getting the value //在设置或获取值之前添加要修复其名称的属性 cssProps: { // normalize float css property // (IE uses styleFloat instead of cssFloat) support.cssFloat = !!div.style.cssFloat; "float": support.cssFloat ? "cssFloat" : "styleFloat" }, // Get and set the style property on a DOM Node 获取和设置DOM节点上的style属性 style: function( elem, name, value, extra ) { // Don't set styles on text and comment nodes 不要在文本和注释节点上设置样式 if ( !elem || elem.nodeType === 3 || elem.nodeType === 8 || !elem.style ) { return; } // Make sure that we're working with the right name 确保我们正在使用正确的名称 var ret, type, hooks, origName = jQuery.camelCase( name ), style = elem.style; name = jQuery.cssProps[ origName ] || ( jQuery.cssProps[ origName ] = vendorPropName( origName ) || origName ); // gets hook for the prefixed version // followed by the unprefixed version hooks = jQuery.cssHooks[ name ] || jQuery.cssHooks[ origName ]; // Check if we're setting a value if ( value !== undefined ) { type = typeof value; // Convert "+=" or "-=" to relative numbers (#7345) if ( type === "string" && ( ret = rcssNum.exec( value ) ) && ret[ 1 ] ) { value = adjustCSS( elem, name, ret ); // Fixes bug #9237 type = "number"; } // Make sure that null and NaN values aren't set. See: #7116 if ( value == null || value !== value ) { return; } // If a number was passed in, add the unit (except for certain CSS properties) if ( type === "number" ) { value += ret && ret[ 3 ] || ( jQuery.cssNumber[ origName ] ? "" : "px" ); } // Fixes #8908, it can be done more correctly by specifing setters in cssHooks, // but it would mean to define eight // (for every problematic property) identical functions if ( !support.clearCloneStyle && value === "" && name.indexOf( "background" ) === 0 ) { style[ name ] = "inherit"; } // If a hook was provided, use that value, otherwise just set the specified value //如果提供了一个钩子，请使用该值，否则只需设置指定的值 if ( !hooks || !( "set" in hooks ) || ( value = hooks.set( elem, value, extra ) ) !== undefined ) { // Support: IE // Swallow errors from 'invalid' CSS values (#5509) try { style[ name ] = value; } catch ( e ) {} } } else { // If a hook was provided get the non-computed value from there if ( hooks && "get" in hooks && ( ret = hooks.get( elem, false, extra ) ) !== undefined ) { return ret; } // Otherwise just get the value from the style object return style[ name ]; } }, css: function( elem, name, extra, styles ) { var num, val, hooks, origName = jQuery.camelCase( name ); // Make sure that we're working with the right name name = jQuery.cssProps[ origName ] || ( jQuery.cssProps[ origName ] = vendorPropName( origName ) || origName ); // gets hook for the prefixed version // followed by the unprefixed version hooks = jQuery.cssHooks[ name ] || jQuery.cssHooks[ origName ]; // If a hook was provided get the computed value from there if ( hooks && "get" in hooks ) { val = hooks.get( elem, true, extra ); } // Otherwise, if a way to get the computed value exists, use that //如果存在获取计算值的方法，请使用该方法 if ( val === undefined ) { val = curCSS( elem, name, styles ); } //convert "normal" to computed value "normal"转换为计算值 if ( val === "normal" && name in cssNormalTransform ) { val = cssNormalTransform[ name ]; } // Return, converting to number if forced or a qualifier was provided and val looks numeric //返如果被强制或提供限定符和val看起来数字 返回时转换为数字， if ( extra === "" || extra ) { num = parseFloat( val ); return extra === true || isFinite( num ) ? num || 0 : val; } return val; } } ); }
参考：
https://developer.mozilla.org/zh-CN/docs/Web/API/Element/currentStyle
https://msdn.microsoft.com/en-us/library/ms535231(v=vs.85).aspx
http://www.cnblogs.com/xiaominwu/p/4348064.html
https://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-OverrideAndComputed