JavaScript Insert HTML Page

If you need to insert a piece of JavaScript into an HTML page, we need to use the <script> tag (and use the type attribute to define the scripting language).

In this way, <script type= "Text/javascript" > and </script> can tell the browser where JavaScript starts and where it ends.

<script type="text/javascript"> ... </script></body> 
The document.write field is a standard JavaScript command used to write output to a page.
After inputting the document.write command into <script type= "Text/javascript" > and </script>, the browser will execute it as a JavaScript command. The browser will then write "Hello world!" to the page.
<script type="text/javascript"> document.write("Hello World!"); </script></body> 
JavaScript Insert HTML Page