cssom

I have read that CSSOM creation is a bottleneck in terms of web page performance. But there seems to be some ways around it, like adding the media property to the stylesheet link. I'm trying to understand how to optimise my web app and came across this really interesting link but couldn't understand what order CSSOM and DOM creation happen in. Here I see some reference to asynchronous loading of CSS files, but the answer is not very clear. Of course, that is about loading and not object model creation. My question is this: Does the CSSOM creation and DOM creation happen in parallel or in

CSSOM 指 CSS Object Model ，即 CSS对象模型 。CSSOM 是 JavaScript 操纵 CSS 的一系列 API 集合，它属是 DOM 和 HTML API 的附属。 其中视图模型（View Model）中定义了一系列接口，包括多个关于窗体、文档和元素的位置尺寸信息，特别容易混淆。 Window 接口 innerWidth/innerHeight 浏览器窗口可见区的高宽，包括滚动条。 outerWidth/outerHeight 浏览器窗口的外边沿宽高。 scrollX/scrollY 文档水平/垂直滚动量。 pageXOffset/pageYOffset 同上。 screenX/screenY 浏览器左上角距离屏幕左上角的距离。 Screen 接口 availWidth/availHeight 屏幕可用区域的尺寸。 width/height 屏幕整体尺寸。 Element 接口 clientWidth/clientHeight 元素本身尺寸，包括 padding，但不包括 border、margin 和 scroll。 因此一个设置了 width:100px 的元素出现宽度为 15px 的覆盖式滚动条后，它的 clientWidth 为 85px。 一些浏览器的滚动条是半透明的，并允许覆盖页面元素，这种情形下，clientWidth 为 100px。

So, I have a DIV #Wrapper which has a fixed width. Inside that DIV, I have another DIV #Panel which also has a fixed width: <div id="Wrapper"> <p>...</p> <div id="Panel">Panel</div> <p>...</p> </div> Sometimes, the width of the Panel is larger than the with of the Wrapper, and in those cases I would like to widen the Wrapper via JavaScript, so that it wraps the Panel perfectly. Live demo: http://jsfiddle.net/H6rML/ I intended to use .scrollWidth on the Wrapper to determine the width of the Panel. However, the problem is that the Wrapper has horizontal padding, and the .scrollWidth for some

Could you tell me why we need to use the getPropertyValue method if we can use only the getComputedStyle one? For example, this will work, as far as I understand: var s = getComputedStyle(element, null).opacity; Which is equivalent to the following: var s = getComputedStyle(element, null).getPropertyValue('opacity'); Can we use getComputedStyle without getPropertyValue ? According to the old DOM L2 Style , getPropertyValue was not required: The CSS2Properties interface represents a convenience mechanism for retrieving and setting properties within a CSSStyleDeclaration . The attributes of this

In Code.org's App Lab editor, we recently started seeing this error in Chrome 64: Uncaught DOMException: Failed to read the 'rules' property from 'CSSStyleSheet' The error is thrown in this function designed to detect whether CSS media queries are being used by the browser, on the line that includes styleSheets[i].cssRules . /** * IE9 throws an exception when trying to access the media field of a stylesheet */ export function browserSupportsCssMedia() { var styleSheets = document.styleSheets; for (var i = 0; i < styleSheets.length; i++) { var rules = styleSheets[i].cssRules || styleSheets[i]