JavaScript/Bookmarklets
Bookmarklets are one line scripts stored in the URL field of a bookmark. Bookmarklets have been around for a long time so they will work in older browsers.
JavaScript URI scheme[edit]
You should be familiar with URL that start with schemes like http and ftp, e.g. http://en.wikibooks.org/. There is also the JavaScript scheme, which is used to start every bookmarklet.
JavaScript:alert('Hello, World!');
Using multiple lines of code[edit]
Since you cannot have line breaks in bookmarklets you must use a semicolon at the end of each code statement instead.
JavaScript:name=prompt('What is your name?'); alert('Hello, ' + name);
The JavaScript Protocol in Links[edit]
The JavaScript protocol can be used in links. This may be considered bad practice, as it prevents access for or confuses users who have disabled JavaScript. See Best Practices.
<a href="JavaScript:document.bgColor='#0000FF'">blue background</a>
Examples[edit]
A large quantity of links may be found on bookmarklets.com, which show a variety of features that can be performed within JavaScript.