A small help, on my project

Hello Friends and Instructors!

I am trying to use the freecodecamp javascript project in DOM. I am doing this project. I tried well. Everything working, but when the user clicks without any input, it gives the message that fields must not be empty. But, need to refresh the page to work its calculation. I mean, if user puts value again without refresh, it doesnt work. Can any one please give me the hints to solve this?
Thank you very much in advance.
@gangalalchapain

@camperextraordinaire Thank you very much sir. I checked console too many time, but could not get idea. Thank you very much.
you are so kind and helpful.

Thank you again Sir.

I created the new DIV for error message and just a small change on script it works perfectly. Thank you very much sir. Thanks for your inspiration and support sir.

@camperextraordinaire
Thank you sir, This is the first time I got the way exactly what I am looking for. This will give me really a good idea to recognize the way of coding what I am looking for in my study. As, I am new in this, I always afraid to do the project, because I think, my code writing is not a real way in practical world. And, thus I am always looking for the way. You give me the way. You do not only give the better solution of the problem, but more and more, you give me the way of solving the problem. I have no words for your sir. Please always motivate the beginner like me in the same way. God bless you and family.
You are the first kind instructor of coding in online learning.
I will study the every step of your coding and will get the way of coding. I will never afraid of coding the project now.
Thank you from my heart sir.