Need a script made in javascript

Need a function made in javascript (though you can use jquery if you want as well, but javascript is preferred). Basically what the script will do is add a button that is found on many mobile sites these days. The 'read full story ' button, as shown here: [login to view URL] However it needs to do things a little bit differently. The button should only be shown if the article is longer than the viewport. If it is, then the code should add a 'read full story' button right at the edge of the viewport. However, If the text content is not longer than the viewport then there should be no 'read full story button'. I can provide more details upon request