HTML5 the definition and stipulation of each label: script

The script tag is used to define client script, such as JavaScript.
In addition to the global properties, there are the following properties

SRC defines the URL to the file that contains the script (so that you can refer to a file that contains the script instead of inserting the script directly into your HTML document)
Async defines whether the script executes asynchronously.
Defer indicates that the script will not generate any document content. The browser can continue to parse and draw the page.
Type Specifies the MIME type default Text/javascript
CharSet defines the character encoding used in the script.

If the Async property is true, the script executes asynchronously relative to the rest of the document, so the script executes in the process of the page continuing parsing.
If the Async property is false and the defer property is true, the script executes after the page finishes parsing.
If both the async and defer properties are false, the script executes immediately, and the page continues parsing after the script has finished executing.
Tip: If the src attribute exists, the &script& label must be empty.

Dom interface

Interface Htmlscriptelement:htmlelement {
           attribute domstring src;
           attribute Boolean async;
           attribute Boolean defer;
           attribute domstring type;
           attribute domstring charset;
           attribute domstring text;
};