javascript:expr=prompt('Formula...(eg: 2*3 + 7/8 )','');if(expr!=null){with(Math){evl=parseFloat(eval(expr))};if(isNaN(evl)){alert('Really are you kidding me?%20Enter%20in%20a%20number,%20not%20that%20shit!%27)}else{alert(evl)}}else{void(null)}