Creating an output using two text fields

Question

Need the output to be this for example- jSmith
After user types in their first and last names into a form's text boxes, the JavaScript will convert their name to look like the example above.
I've included the code I've done so far. Appreciate the help
https://code.sololearn.com/WoFqOlkaHYcu/?ref=app

Answer 1

res variable is repeated two times
and to take the value from html it should
only be written "form name.any name.value" avoid
writing document.