This bookmarklet gives you a code editor in your browser with a single click.

notepad.html

data:text/html, <style type="text/css">html,body{height:100%;margin:0;padding:0}.e{height:100%}</style><div class="e" id="editor"></div><script src="https://cdnjs.cloudflare.com/ajax/libs/ace/1.2.9/ace.js" type="text/javascript" charset="utf-8"></script><script>var e=ace.edit("editor");e.setTheme("ace/theme/monokai");e.getSession().setMode("ace/mode/javascript");</script>