how do i make a simple calculator using may be buttons assigned to a given class name?

Question

i have tried to make one with the basic knowledge of document. getElementsByClassName() but it shows undefined... i know it may seem funny.. but its the idea i had in mind... Any help?

Answer 1

https://code.sololearn.com/WN0dgrcEv5FY/?ref=app

https://code.sololearn.com/cXD3ve2VxfP8/?ref=app