It is mainly divided into two parts: the rendering engine (layout engineer or Rendering Engine) and the JS engine.
Rendering engine: responsible for obtaining the content of the web page (HTML, XML, images, etc.), organizing the information (such as adding CSS, etc.), and calculating the display method of the web page, and then outputting it to the monitor or printer. Different browser kernels will interpret the syntax of web pages differently, so the rendering effects will also be different. The kernel is required for all web browsers, email clients, and other applications that need to edit and display web content.
JS engine: Parse and execute javascript to achieve dynamic effects of web pages.
At first, the rendering engine and the JS engine were not clearly distinguished. Later, the JS engine became more and more independent, and the kernel tended to only refer to the rendering engine.