What's wrong here?

Question

class Add {
constructor(...words) {
this.words = words;
}
//your code goes here

print(){
for(let i of this.words){
this.str += "

Answer 1

Save code and share link here.. That's helps to debug code for errors if any...
edit:
Bezu Tadesse
this.str += "quot;+i;
before this this.str is undefined.
declare it before you using ....