call func if valid and exists

/* Call function IF AND ONLY IF IT EXISTS AND IS VALID otherwise return as undefined */
function chcalc(name) {chcalc:{
  try {
    eval(name)
  } catch(err) {
    break chcalc
  }
  if (typeof eval(name) == 'function') {
  eval(name)();
  }
}}

// Minified Version:
/*

function chcalc(name){a:{try{eval(name)}catch(err){break a}"function"==typeof eval(name)&&eval(name)()}}

*/