How to Put a JavaScript Into an HTML Page

The code above will produce this output on an HTML page:
"Hello World!"

Example Explained

To insert a JavaScript into an HTML page, we use the script tag. Inside the script tag we use the "type=" attribute to define the scripting language.
So, the script type= text/javascript and script tells where the JavaScript starts and ends:

The word document.write is a standard JavaScript command for writing output to a page. By entering the document.write command between the tags, the browser will recognize it as a JavaScript command and execute the code line. In this case the browser will write Hello World! to the page.

Note: If we had not entered the 'script' tag, the browser would have treated the document.write("Hello World!") command as pure text, and just write the entire line on the page.