notcomplex.js

function getData(text){
  var commandAndArgs = text.split(" ");
  var command = commandAndArgs[0];
  var args = commandAndArgs[1];
  var arrayOfArgs = args.split("_");
  var arg1 = arrayOfArgs[0];
  var arg2 = arrayOfArgs[1];
  if(command == "calc"){
    return arg1 - arg2;
  }
  else{
    return false;
  }
}

if(getData("calc 2_1")){
  console.log(getData("calc 2_1"));
}