Tryit Editor v1.8

Source Code:
<!DOCTYPE html> <html> <head> <script src="../../ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"> </script> <script> $(document).ready(function(){ $("button").click(function(){ $("img").attr("width",function(n,v){ return v-50; }); }); }); </script> </head> <body> <img src="img_pulpitrock.jpg" alt="Pulpit Rock" width="284" height="213"> <br> <button>Decrease image width by 50px</button> </body> </html>
Result:
W3Schools.com - Try it yourself