What is Bookmarklet / what is use of Bookmarklet

Each bookmarklet is a tiny program (a JavaScript application) contained in a bookmark (the URL is a "javascript:" URL) which can be saved and used the same way you use normal bookmarks. The idea was suggested in the Netscape JavaScript Guide.

JavaScript has been used by page authors on millions of webpages; Bookmarklets allow anybody to use JavaScript - on whatever page you choose (not just your own page).

so A bookmarklet is an applet, a small computer application, stored as the URL of a bookmark in a web browser or as a hyperlink on a web page. The term is a portmanteau of the terms bookmark and applet. Whether bookmarklet utilities are stored as bookmarks or hyperlinks, they are designed to add one-click functionality to a browser or web page. When clicked, a bookmarklet performs some function, one of a wide variety such as a search query or data extraction. Usually the applet is a JavaScript program.

Web browsers use URIs for the href attribute of the < a > tag and for bookmarks. The URI scheme, such as http:, file:, or ftp:, specifies the protocol and required form for the rest of the string. Browsers also implement a prefix javascript: that to a parser is just like any other URI. Internally, the browser sees that the protocol is javascript, treats the rest of the string as javascript code which is then executed, and uses the resulting string as the new page.

The executing script has access to the current page, which it may inspect and change. If the script returns an undefined type (rather than, say, a string), the browser will not load a new page, with the result that the script simply runs against the current page content. This permits in-place font size and color changes, for example, without a page reload.

An anonymous function can be used to force the script to return an undefined type:

javascript:(function(){
/* Statements returning a non-undefined type, e.g. assignments */
})();


Bookmarklets are saved and used as normal bookmarks. As such, they are simple "one-click" tools which add functionality to the browser. For example, they can:

- Modify the appearance of a web page within the browser (e.g., change font size, background color, etc.).
- Extract data from a web page (e.g., hyperlinks, images, text, etc.).
- Submit the current page to a blogging service such as Posterous, link-shortening service such as su.pr, or bookmarking service such as Delicious.
- Query a search engine, with search term(s) provided by previously selected text, or by a dialog box.
- Submit the current page to a link validation service, or translation service.
- Set commonly chosen configuration options when the page itself provides no way to do this.

Bookmarklets are safer than traditional software for the following reasons:

- They are extremely simple. With only a few lines of code it's hard to make a programming error that isn't detected immediately.

- You don't install software. Traditional software programs can produce conflicts with other programs on your hard drive. Bookmarklets work entirely within your web browser, so they can't independently interfere with the functioning of other programs.

- Even if something goes wrong (say, you try to use a Netscape-only bookmarklet on Internet Explorer) the worst thing that is likely to happen is that you will get a JavaScript error message. Furthermore, this site has been designed (through server-side scripting) to make it impossible for you to get a bookmarklet that doesn't work on your browser.

- Because you don't install software, you don't have the security risks of traditional software (which can install files all over your hard drive). Your hard drive is protected by JavaScript security restrictions.