FCC BAS #38 - Bonfire: Arguments Optional

function add() {
    //if any given value is not a number it will return udefined
    for (var i = 0; i < arguments.length; i++){
        if (typeof arguments[i] !== 'number') {
          return undefined;
        }
    }
    
    //store first argument into var 'num'
    var num = arguments[0];

    //if there is only 1 argument check if there is another
    if (arguments.length === 1) {
        return function(x){
          for (var i = 0; i < arguments.length; i++){ //make sure its a number
                if (typeof arguments[i] !== 'number') {
                    return undefined;
                }
            }
          return x + num; //add the second given argument
        };
    } else {
        return num + arguments[1]; //return if originally given 2 arguments
    }
}

add(2)(3);