It looks like you have placed the string ‘letter’ inside of the print() statement instead of the variable letter. Which is why the app is printing out ‘letter’ for every letter in ‘grasshopper’ rather than actually printing out the letter to spell out ‘grasshopper’.
for (var letter of 'grasshoper')
This loops through grasshopper, with every run, a letter is assigned to letter in order of the string. So for the first run, letter === ‘g’, then letter === ‘r’, then letter === ‘a’, etc. All the way until the loop reaches r, prints ‘r’, then the loop ends.
Hope this helps!