I think you need to be really careful about the names of your functions vs what you're asking for - your question with 'append' string, yet you've named your function 'prependToString', and have 'appendToString in the console write - they are two different results
So, how do you write a function in javascript ? maybe ....
function appendToString() {
}
but that's not going to work without parameters is it ?
function appendToString(base, append) {
}
ok, but it doesnt do anything nor return anything yet
function appendToString(base, append) {
var res = base.SOMETHING(append)
return res
}
so, how do you combine strings in javascript - look it up either in your textbook or google 'javascript combine string', and where I have put 'base.SOMETHING' above, make 'SOMETHING' the correct function .. this isnt hard, but you really need to read your textbook and apply yourself a bit