JavaScript Advanced Programming (Third Edition) Chapter II using JavaScript in HTML

2.1 <script> Element <script> defines the following 6 properties:

• Async: Optional. Indicates that the script should be downloaded immediately, but should not interfere with other actions on the page, such as downloading additional resources or waiting for other scripts to load. Valid only for external script files.
• CharSet: Optional. Represents the character set of the code specified by the SRC attribute. Because most browsers ignore its value, this property is seldom used.
• Defer: Optional. Indicates that the script can be deferred until the document is fully parsed and displayed before execution. Valid only for external script files. IE7 and earlier versions of this property are also supported for embedded scripting.
• Language: Deprecated.
• SRC: Optional. Represents the external file that contains the code to execute.
• Type: Optional. Represents the content type of the scripting language in which the code is written.

The <script> element with the SRC attribute should not contain additional JavaScript code between its <script> and </script> tags. If embedded code is included, only the external script file is downloaded and executed, and the embedded code is ignored.

2.3 Document Mode

The first two document modes: Promiscuous mode and Standard mode

2.4<noscript> elements

<noscript> elements to display alternative content in browsers that do not support JavaScript

JavaScript Advanced Programming (Third Edition) Chapter II using JavaScript in HTML