Detailed explanation of Javascript asynchronous loading (browser loading method in javascript)_javascript skills

1. The forms of synchronous loading and asynchronous loading
1. Synchronous loading
The most commonly used form of synchronous loading is this:

Synchronous mode, also known as blocking mode, will prevent the browser from subsequent processing, stop subsequent parsing, and therefore stop subsequent file loading (such as images), rendering, code execution.
The reason why js needs to be executed synchronously is because there may be behaviors such as outputting document content, modifying dom, redirection, etc. in js, so synchronous execution is safe by default.
The previous general recommendation was to place <script> at the end of the page before </script>