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<!DOCTYPE html> <html> <head> <script src="/lib/jquery-1.12.2.min.js"></script> <script> $(document).ready(function(){ $("button").click(function(){ $("li").toggleClass(function(n){ return "listitem_" + n; }); }); }); </script> <style> .listitem_1, .listitem_3 { color: red; } .listitem_0, .listitem_2 { color: blue; } </style> </head> <body> <h1>This is a heading</h1> <ul> <li>Peter</li> <li>Lois</li> <li>Chris</li> <li>Stewie</li> </ul> <button>Add/remove classes to list items</button> </body> </html>