问题
When I inspect a website,
I see the cssRules from document.styleSheets[x].cssRules
However, with this website stackoverflow.com, when I inspect with Chrome browser, I see document.styleSheets, but cssRules is null.
How come this is possible?
回答1:
That's because the style sheets are coming from a different domain. Some browsers (such as Chrome) implement strict cross-domain policies by throwing security errors or setting the cssRules and ownerRule to null when it comes from a different domain...in your case the style sheets come from a CDN
MDN quotes the following in the CSSStyleSheet documentation...
In some browsers, if a stylesheet is loaded from a different domain, calling cssRules results in SecurityError.
https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleSheet
来源：https://stackoverflow.com/questions/46356349/document-stylesheetsx-cssrules-are-null