JavaScript Advanced Programming (3rd Edition) Chapter II (using JS in HTML)

1.script element Properties (6): ①async (Asynchronous script), valid only for external scripts

②defer (deferred script), valid only for external scripts

③CHARSET,SRC (cross-domain), type,language

2. Use external JS files whenever possible, because the browser caches all external JS files according to the settings. That is, if you have 2 pages that use the same file, you only need to download the file once

3.①js scripts are generally placed in front of </body>. So that the content of the page after rendering, then parse JS.

The ②async property, which represents the current script, does not have to wait for other scripts or block document rendering.

The ③defer property, which represents the current script, needs to be executed after the document rendering is complete.

Example: 1 <div> 2 <script></script> 3 </div>

JavaScript Advanced Programming (3rd Edition) Chapter II (using JS in HTML)