Javascript insert style implementation code _ javascript skills

A recent project requires javascript dynamic insertion styles, and the previous method becomes invalid! The reason why I checked it for two hours turned out to be my own bid. In the end, the javascript insertion style is widely used in front-end development, especially when I modify the front-end performance and page skin-changing. Recently, When you click a button on another website, a script is inserted and executed on another website page, which includes style insertion.

In general, there are two types of javascript dynamic insert styles. One is to introduce an external style to a pageUsed in Label introduces an external style file, and the other is to use