The modern understanding of a web page is that it consists of three distinct
parts:

1. Content (HTML)
2. Presentation (CSS)
3. Behavior (JavaScript)

These should be kept separate, ideally each in its own file (or files). What
it means for JavaScript is that there should be no inline such as onclick,
onmouseover, etc. Ideally there should be little to no inline scripts.

The idea is that content (the text on the page) is independent of:

• how it looks like, so the page should be usable even with CSS disabled, or not supported by the browser, and
• how it behaves, meaning the page should be usable even with JavaScript disabled. The content should be accessible independent of any mouseovers, animations, and so on.

也就是说：

我们使用js框架将结构（HTML）和行为分离(JS)，用css将结构和表现分离

其他：

HTTP has two hurdles to address. It is stateless , and it is text
based .