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13.2.5.1 Bookmarklets

13.2.5.1 Bookmarklets


In a web browser, a “bookmark” is a saved URL. If you bookmark a javascript: URL, you are saving a small script, known as a bookmarklet. A bookmarklet is a mini-program that can be easily launched from the browser’s menus or toolbar. The code in a bookmarklet runs as if it were a script on the page and can query and set document content, presentation, and behavior. As long as a bookmarklet does not return a value, it can operate on whatever document is currently displayed without replacing that document with new content.

Consider the following javascript:URL in an tag. Clicking the link opens a simple JavaScript expression evaluator that allows you to evaluate expressions and execute statements in the context of the page:

JavaScript Evaluator


Note that even though this JavaScript URL is written across multiple lines, the HTML parser treats it as a single line, and single-line // comments will not work in it. Also, remember that the code is all part of a single-quoted HTML attribute, so the code may not contain any single quotes.

A link like this is useful when hardcoded into a page that you are developing but becomes much more useful when stored as a bookmark that you can run on any page. Browsers typically allow you to bookmark the destination of a hyperlink by right-clicking on the link and selecting something like Bookmark Link or by dragging the link to your bookmarks toolbar.

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