Javascript loading and execution-performance improvement_javascript skills

The blocking nature of Js
The performance issue of Javascript in the browser may be the most important usability issue
The blocking nature of Js The browser uses a single process to handle the UI process and the execution of Js
Whether it is embedded or external, download and execute immediately because it may modify the page

The concept of page life cycle
The download time and executing time
Nothing will be output until the script and link body are loaded in the head, so you will see a blank page