Create a function that sums two arguments together. If only one argument is provided, then return a function that expects one argument and returns the sum.

partialfunction.js

function add() {
  function checkNum(num) {
    if (typeof num != 'number') {
      return false;
    }
    return true;
  }
  if(arguments.length == 1) {
    var c=arguments[0];
    if (checkNum(c)) {
      return function(arg2) {
        if(checkNum(arg2)) {
          return c + arg2;   
        } else {
          return undefined;
        }
      }
    } else {
      return undefined;
    } 
  } else {
      if(checkNum(arguments[0]) && checkNum(arguments[1])) {
        return arguments[0] + arguments[1];
      } else {
        return undefined;
      }
      
  }
}

add(2,3);