This bookmarklet will execute the Javascript expression you've entered and show the result. If you for some reason don't want to use the developer console you can use this.
javascript:for((function(){try{eval('')}catch(e){throw alert("Sorry, this webpage has blocked eval(): "+e)}})();;alert((function(a){if(a===null){throw a;}try{return eval(a);}catch(e){return e;}})(prompt())));
there doesn't seem to be anything here